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If you can wait until early 2013 then sure. If not, then the 3570K is a good upgrade from the PII. Have you overclocked it?
There's hardly difference between PCI-E 2.0 and 3.0 for gaming, so no not really.
What sort of BSODs are you getting? Have you checked temps? Different set of GPU drivers (12.3 is the most stable AMD drivers for me at the moment)?
I just upgraded last week from an AMD 955BE stock, i had it coupled with a HD5850, and in the likes of skyrim looking down on the town in Whiterun id get around 12 to 17FPS. i did the same thing with the intel 3570k and the same Graphics card this time with the settings in game higher (draw distance etc) and its no lower than 54FPS at the same spot in Whiterun, i also no longer get stuttering running around etc. my Skyrim is slightly modded too with texture pack and better waters and snow etc.
Well, I moved from a 965 @ 3.8ghz to a 2600K @ 4.4ghz, and all the CPU dependant games felt more smoother thanks to the higher minimum framerates.