Even though the FX CPU does have 8 cores its not as power efficient and it's just not as powerful as the 3570k. Yes, the 8 cores aren't supported in most things so as other things progress it will preform better but it will still be lacking. I would go with the 3570k because they are more power efficient and it's hyper threaded so for the most part it preforms like a 8 core CPU.
The i5 for desktop processors do not have hyper threading. Having said that, as a computer salesperson who sells probably 1k-1.5k processors a year, go with the i5. It's a 4 core, but each core can do SO much more than the bulldozer can.
Having said that, I'm not saying bulldozer is slow.