Just want to correct you on the 3770K being great for OC. It's not. It gets hot as hell and your whole PC turns to slug if you try to go higher than 4,6. At 4,6 even the h100i will have trouble keeping it cool. How do I know? I bought one, overclocked it for a few weeks and stuck my 2600K back in as it allows me 4,9ghz with no issues. a 2600K beats a 3770K easily when both are overclocked to their limits.
The 3570K however is a nice little CPU that will do the job you want it to do, although a tiny bit slower but you won't notice that. Only way you will notice the difference between the i7 and i5 is if you are using autocad alot, i mean hours a day. Also, HT makes the cores, physical and logical, a tiny bit less effective than if it wasn't HT. That means that single threaded operations will work better clock for clock on the i5 vs the i7(games and most programs). Only reason the i7 marginally wins in performance at stock speed is due to higher base clock, if they were the same speed the i5 would reign supreme.
Luckily, overclockin fixes the problem for the i5 as you will easily OC it to 4,3 and beat a stock i7 at everything but autocad. In real life though, the only place you can tell the difference between them is in 3Dmark and other benchmarking tools, no chance you can tell the difference in games.