My office computer runs Windows 8.1  on  AMD 3 core 3.4- 4 Gigs RAM, my son built it for under $500 including a good case.
I installed a second version of Sonar X3 on it as a studio back up plan. I don't use it for Sonar but I loaded a big project, mucked about for and hour and it seemed very stable. 
I do a lot of MS Office stuff, Photo Shop, Movies, I burn my CD's and work in Wave Lab on this machine.  I've owned a few AMD computers and never noticed any difference. It is pretty fast and multi tasks smoothly. One thing is if you run DPCLAT it's stuck at 1,000 which seems to be a W 8.1 issue with the DPCLT test. 

It's not a bad idea to get the best you can afford. I would go for the 3.0 Ghz cpu though it's only a slight performance increase, do know that higher CPU speed will also help with better low latency performance, and of course better performance with additional plug ins in projects. My thinking is a person shoould go for the best performance they can afford.
 
If you change your CPU and motherboard, that may be more money you would have to spend for new compatible memory.

robert_e_bone
I don't know if you have looked at them, but AMD has some GREAT CPU/Motherboard bundle deals at Micro Center, and you can get a CPU and a motherboard that are about on par with an Intel i5 for quite a bit less.  (about $100 cheaper, I believe)
 
...
 
Bob Bone

 
Thank you for the recommendations, Bob. Were I building an all new machine from scratch, I would surely give great consideration to that route. But I'm really not looking to get that in depth and have to reinstall Windows and all of that at this point in time. I honestly should be satisfied with just a modest update to my current setup for right now.
 
 

Leadfoot
I would say that if the extra $30 doesn't hurt your budget too badly, you might as well get the Q9650. $175 still seems like a good price compared to the $500 or so that I spent on the Q9550 when it was a new model.

CakeAlexS
Hardly will make any difference, but you know you will want that 6% increase for $30 just to keep you happy.

I think most people who are on machines since Windows 7 came out probably use under 8Gb memory and half their CPU most of the time (not all of you before you all start posting, there are obviously use cases!).
 
Cheers...

thomasabarnes
It's not a bad idea to get the best you can afford. I would go for the 3.0 Ghz cpu though it's only a slight performance increase, do know that higher CPU speed will also help with better low latency performance, and of course better performance with additional plug ins in projects. My thinking is a person shoould go for the best performance they can afford.

 
Technically speaking, I CAN afford the extra $30 without breaking the bank. But I also like to save a few bucks whenever I can... That's why the main question running around inside my head is: Would I notice any difference between the two?... Be it with functionality, latency, or anything else. If yes, then I would have to consider the 9650 more seriously. If no, then I think I would probably prefer to save the cash and just go for the 9550, even at the expense of the psychological satisfaction of an extra 0.17 GHz, tempting though it is...

man im still running a  q6600 at 2.4 ghz x 4, any of those chips will do the job, surely you could get an i7/i5 for roughly the same price

You personally would not notice any difference as neither one would be called upon to run at max output for any length of time. Basically they're just numbers. Individual processors may or may not give you those exact speeds anyway since they're just averaged for marketing labels more than anything.
 
Makes me think of the auto industry back in the day when 402s were being labeled and sold as 396s (basically the same engine) cause the 396 had such a reputation and they were afraid people would be scared off by "the new and unknown". Really?!
 
On the other hand if you can afford it and it requires no other changes in hardware I'd go for the bigger one, but only for psychological reasons.

.

Just checked the build notes from my previous PC. That was a Q9550. It hardly ever went over 70%, though I rarely use software synths so perhaps wasn't pushing it that hard.

My current i7 barely breaks into a sweat most of the time. It does however give me much better round-trip latency times.

Once c. 3GHz quad-cores appeared system speed and efficiency pretty much moved away from raw cpu power being the DAW performance bottleneck. The otther components, especially the HDD controller, became of equal importance.

Well, I have had concurrent computers for years now, with my primary running an i7 CPU with 32 GB of memory, and that rocks.  The secondary computers is running an AMD CPU with 16 GB of memory, and that rocks too.
 
Both of the above have ZERO performance issues when running Sonar and a bunch of soft synths and audio tracks.
 
The AMD computer was way cheaper than the i7, and does fit the bill nicely, and I would not hesitate to look at building my i7 replacement computer with an AMD CPU instead of Intel.
 
I just looked a moment ago at the Micro Center AMD CPU and motherboard bundles, and if I were to build my own computer this weekend I would choose from the following:
 
1.  AMD FX 8350 CPU with a nice bundled motherboard for $199-$207 together, depending on which motherboard I would choose.  This processor has EIGHT cores and runs at 4 GHz.  The motherboards all have USB 3, and USB 2, and all the goodies I would need.
 
2.  AMD FX 8230 CPU and bundled motherboard for $170 together, choosing from the same available motherboards as above.  This CPU also has EIGHT cores, and runs at 3.5 GHz, and is unlocked and can run in turbo mode at 4 GHz (but I would not overclock it myself, from a matter of personal choice).
 
3.  AMD FX 6350 CPU and bundled motherboard for $160-$180 together.  This one has SIX cores and runs at 3.9 GHz, and can be overclocked as well.
 
4.  AMD FX 6320 CPU and motherboard for $140-$160 together.  SIX cores and 3.5 GHz, and can be overclocked.
 
My most likely choice would be the AMD FX 8350 CPU, with its 8 cores and 4 GHz speed.  This CPU is on par with an i5 Intel CPU, to the best of my knowledge, and again, I have run far less capable AMD CPU's and Sonar for years with no problems.
 
I would save AT LEAST $100 just on the cost of the CPU, going with AMD instead of Intel.
 
Bob Bone
 

As as noted by someone else above, the multiple-core CPU's all run plenty fast enough for Sonar, and so it largely comes down to where you want to spend money.
 
I would rather save money on getting a less expensive AMD CPU and motherboard, and invest that $100 or more of savings into another 8 GB of memory, or for about $20 more and using that $100 of savings, I would have enough just with that to buy a 120 GB solid-state drive and a 2 TB 7,200 SATA III HD.
 
I wish you the best of luck in any event, and hope you are able to fit the budget and hardware pieces together to end up with a solid computer that meets your needs.
 
Bob Bone
 
Bob Bone
 

thomasabarnes
... I would go for the 3.0 Ghz cpu though it's only a slight performance increase, do know that higher CPU speed will also help with better low latency performance ...

 
Would the 6% increase from the 2.83 Ghz to the 3.00 GHz equate to a 6% improvement in latency?... More generally, does latency performance always utilize 100% of a processor's capabilities?
 
And one last quick question: These two processors are both rated at the same TDP wattage. I know that as a general rule of thumb, the higher the performance of a chip, the hotter it will run. But should it be expected that this 3.00 GHz chip would run any hotter than the 2.83 GHz, seeing as they are otherwise virtually identical and the difference in clock speed is so small?