New computer, Haswell or Sandy or Ivy?

My suggestions to anyone that asks is "buy overkill" or "as much as your pocketbook can stand".  It won't be needed now, but down the line you will be glad you did. 
 
My new (last year) system that I built has an i7 3770 CPU.  Its probably along the lines of what you want and not break the bank.  (see my sig).

Well, it is always nice to have the latest and greatest version of everything computer, even if it will only be current for 6-18 months. But like buying a new car every year, it may not be the most cost effective way to get to work. Buying the best, newest or greatest computer is usually a symptom of not knowing what you need and using your hard earned (or easily inherited) money instead of your precious time to make a rational decision. If you have a ****load of money to spend on a DAW, I suggest that you go to one of the better professional DAW assemblers and buy their hottest newest workstation. That way you are relatively certain that incompatibilities have been weeded out, and you will get a reasonably current functioning DAW.
 
The only good reason for building your own system is to save a little money, and avoid the disaster that frequently accompanies buying a machine that was designed to play games or run complex graphics software. You will not save any money buying the newest components at retail, and you will not save any time researching the individual components. I have always built my own systems, but never using hottest most recent most expensive components, and have managed to save a little money and spend a lot of time. Since I have no income, that is a reasonable bargain considering the little time I have left.
 
The first question to ask yourself is what problem you are currently having running your software on an 8 GB system. If you are not having problems, it is not time to upgrade to a system that will be obsolete by the time you start to have problems.
 
The next is what kind of software you plan to run. Not just Sonar, but are you using samplers or synths and how many and how much processing of how many tracks. For most audio applications raw processor speed is more important than a gazillion cores.

The main difference between the i7 3770 and the i7 3770K, beside the $$ is the K is more for overclocking.  I don't overclock or plan on it so the i7 3770 was right for me.
 
the i7 3770 is a "Quad Core" but its a "dual quad core" (best I can describe it), thus it operates as 8 cores.
 
 

ok time to get some facts correct..
 
1) someone mentioned that Haswell is NOT an improvement over Ivy this is completely incorrect
 
http://www.gearslutz.com/board/music-computers/829104-prelim-haswell-benchmarks.html
Haswell does run a bit hotter than Ivy but with the right cooler is no issue.
 
you only real options are Haswell or Ivy E. it would be foolish to buy older.
 
Ivy-E is no better than Sandy-E performance wise but runs much cooler (NOT hotter)
http://www.gearslutz.com/board/music-computers/866352-preliminary-ivy-e-benchies.html
 
Haswell vs Ivy-E :
the basic raw performance for most is pretty close. if you are not a heavy samples user (real samples not synths)
or doing massive effects and crazy 96K track counts then just buy the Haswell.
you want the best of the best get the 4930K
either one you want to over clock.