In addition to Arris's very informative comments at # 8; I'd like to add just one more thing, games which are CPU intensive will see 'less' of a performance boost, whereas, games which are not CPU dependent will get higher performance boost.
Good plans Arris, I am thinking about upgrading my system as well to i7 2600, not that I need it frankly; I guess because I'm bit annoyed with this motherboard which can only take in 4 GB of ram (the original DP35DP died, went back into warranty, died again, and then they made me buy a miniATX board as full ATX for LGA775 were no longer available).