Well mate, with the kit you have I would say easily 3.4GHz, with no problems at all.
3.6GHz, should be fine. I can get this stable on a i7 920 running prime95 for 7 hours, then got bored and played games. So a 930 should be more then ok. I believe you can reach this at stock voltage if you have a decent chip, maybe a tiny increase otherwise. this should not effect temps much.
3.8GHz. Should be doable with out to much hassle and tweaking. I'm currently managing this on my CPU. I play BC2 for about 4 hours at a time, Total war Napoleon for a few hours at a time, Supreme commander II for several hours at a time, and even METRO2033 stable for 2 hours. Non of them have ever crashed.
Although it nice to overclock, cos you feel like your getting way more then your moneys worth, with the graphics card you have you wont notice much if and difference in games. Your card will bottle next everything else. 2 high end cards will make you use more CPU, but even then your stock is probably high enough. I'm yet to play a game that come anywhere near maxing my CPU out. I'd say on average most high end games hit around 75% of CPU but it troughs and peaks alot.
If you use dual screen, on the spare screen run MSI Afterburner, and CORETEMP, and a gadget that will show your core speeds. I bet whatever game you play MSI afterburner will show your GPU working way harder then your CPU ever will.
Your air system sounds good, so if you wanna overclock go for it mate. I think 3.6GHz would be a sweet spot for you unless you want bragging rights to your mates :O)