Des,
 
I too remember the first hard drives that came out for the IBM PC.  It was 10 MEGS and cost well over $1000.  I remember a guy that upgraded his IBM PC to 128 MEGS of RAM and it cost him $2000.  All this was in the mid 80s.  
 
When I think of TB hard drives, it amazes me on how much data this truly is.  I think the technical advances in hardware has made software engineers job a lot easier.
 
Jim

Running one core less makes sense. Audition does similar (one core less) automatically and is very obvious when doing batch processing. The core program runs on one core and each batch process gets its own core. It also has merit not to process on Core 0 because a lot of Windows defaults to that (every computer has a Core 0 so is a safe "default" for any program).

But... I am not sure if you specify one core less how SONAR actually acts upon that... there is no choice of "which" cores, just how many.

You should also remember that the motherboard plays a role here. E.g. there are differences as what the DPC latency is.
 
This is the fastest in the market (by Anandtech) with a list of some slower ones --- and there are some really slow ones on the market at the entry level. The difference may be day-and-night.
 
DPC Latency
Deferred Procedure Call latency is a way in which Windows handles interrupt servicing. In order to wait for a processor to acknowledge the request, the system will queue all interrupt requests by priority. Critical interrupts will be handled as soon as possible, whereas lesser priority requests such as audio will be further down the line. If the audio device requires data, it will have to wait until the request is processed before the buffer is filled.

Jyri T.
You should also remember that the motherboard plays a role here. E.g. there are differences as what the DPC latency is.
 
This is the fastest in the market (by Anandtech) with a list of some slower ones --- and there are some really slow ones on the market at the entry level. The difference may be day-and-night.
 

Absolutely agree that DPC Latency (low/consistent) is critical to low latency audio performance.
 
That said, I question the results reported in the above link.
I've measured the results with several of the listed motherboards... and DPC Latency is *not* that high.
You don't have to spend $500 on the motherboard to achieve low/consistent DPC Latency.  
 
Aside from the motherboard component drivers, your video card drivers can also have a major impact on DPC Latency.