Yes, I used Tony's site for the previous builds. But their current customized hacks are way out of my price range. So I am left going to the used market, I think. Would a sandy bridge 2600k (over clocked), matching mother board, etc etc, be a significant upgrade over the i7 960?
Here's where the i7 960 scores on Passmark's CPU benchmarks:
http://www.cpubenchmark.net/cpu.php?cpu=Intel+Core+i7+960+@+3.20GHz&id=838
It's at nearly 6,000 and the i7 2600K is up around 8,500. (An i5 2500K is around 6,500 by the way).
The problem with a 2600K is that they're simply too expensive to bother with at this point. On eBay, Amazon and other sources they're selling for $300-$400. If you got one used, I'd say it wouldn't be worth it unless it was extremely cheap, say around $150 or less.
Meanwhile, any chance you live near a Microcenter?
They have the i7 4770 for $239
http://www.microcenter.com/product/413249/Core_i7_4770_34GHz_Boxed_Processor
and even better (if you're lucky enough to live near a store that has one)
the i7 4770K for $250
http://www.microcenter.com/product/413248/Core_i7_4770K_35GHz_Socket_LGA_1150_Boxed_Processor
The 4770K benches at 10,300
http://www.cpubenchmark.net/cpu.php?cpu=Intel+Core+i7-4770K+@+3.50GHz&id=1919
Even for $100 more than the microcenter in-store price (which is its normal price) it's a hell of an upgrade from your 960, almost doubling the CPU power you're currently using.
Are you doing an upgrade of your 960 system, reusing the RAM, case, PSU, drives, etc? If so, you could upgrade just mobo and CPU within your budget.
You could for example use this motherboard:
GA-Z87-HD3
http://www.amazon.com/dp/B00D94X6AK/...nymacx86com-20
Paired with a 4770K:
http://www.newegg.com/Product/Produc...82E16819116901
costing you roughly about $470. (Assuming you couldn't score the CPU at a Microcenter price.) Replacing with parts in your 960 system, this is an upgrade that would nearly double your processing power.
Keeping within your $800 budget (which is extremely low-ball for the level of system you're wanting) you'd have $330 left over to work out your graphic card and monitor needs.