How much of a difference will an I7 or Xeon processor make over an I5.

That can be a loaded question, but in terms of benchmark values, this is a good site to see benchmarks versus CPU cost. Bear in mind that as a sysem, the CPU is only one part of the greater whole.

i7 has more threads (physical and virtual cpu) so effectively can do more multitasking. Xeon is a workstation CPU and can run in parallel with another using SMP (Symmetric Multiprocessing) which requires dedicated RAM per processor. So won't provide you with a great benefit probably unless you are going to be working lots of number-crunching and server applications. IMHO
 
In DAW terms that could be a sequencer with lots of hardware and external input. Hope that summarises it.
 
 

There are many quad core i5s and also dual core i7s so as mettelus pointed out, it can be a loaded question. Generally speaking more cores (even virtual ones) are better for DAWs.

tonyzub999
How much of a difference will an I7 or Xeon processor make over an I5.

For DAW purposes, a Xeon CPU brings *zero* benefit.
In fact, if the clock-rate is significantly lower, you'll take a significant performance hit.
Don't want to sacrifice significant clock-speed for more cores.
In a perfect scenario, high clock-speed *and* more CPU cores.

I think the only exception to that rule is that there are more multiple CPU mobo's for Xeon and Xeons with more cores than the 6 maximum in the i-series, correct?

The only disadvantage I can see is 32 PCI lanes. So if you use a dedicated GPU that leaves 16 split between the rest of the devices. However with x4 and x8 being other bus options and providing no lanes get shared or disabled by use of another. It shouldn't be much a hinderance. They have massive memory support although perhaps the memory speed is an issue. So not for gamers however if it was more affordable and in the right scenario of these could make an excellent workstation. I mean 20 physical cores....geez you could run 300 plug-ins and Sonar will still be like a demanding girlfriend.
 
Having said that, an i7 or i9 if you money will stretch that far will be a better option in the long run.
 

Thanks everyone. I have a decent understanding of computers, but trying to decide on whether to go power laptop alone or decent laptop and desktop is driving me crazy along with trying to retrofit my Liquid Saffire 56 to a PC laptop. I just want to get back to making music. I can use all the technical help I can get.

Something to think about regarding the number of CPU cores and laptops/desktops.
 
In the desktop version, i5 and higher are usually quad-core, but in laptops, you could only end up with a dual core.  They do that for power saving and extended battery life, but at the potential expense of performance.
 
For instance I have an i5 laptop (non DAW), but it is only dual core with 1.7GHz turbo to 2.5Ghz.  It is slower than my i3 desktop (DAW), which is dual core and locked to 3.4 GHz.  Both have 4 threads due to hyperthreading.
 
So I would say at least an i5 quad-core in the 3-4 GHz range would be worth looking at. 
 
The clock speed is the bottom line as far as how fast a single thread can perform.  The more cores/threads you throw at it, the more work your CPU can do concurrently.  The i7 is ideal for a heavily loaded Sonar DAW due to the plugin load balancing with 4 cores/8 threads. 
 
But is up to the software developer to take advantage of multiple cores/threads.  A badly coded app that is single threaded can only run as fast as your max CPU clock speed.  The other cores will not help in that case.

Sanderxpander
I think the only exception to that rule is that there are more multiple CPU mobo's for Xeon and Xeons with more cores than the 6 maximum in the i-series, correct?

The new i9 7900x is the best of all worlds (expect cost).  
10 cores at 4500MHz