the X2 wouldn't just kill the celeron, it would torcher it first.
get a core 2 duo though. they're much better. just sold my X2 3800+ which was overclocked to a 5000+ (2.6ghz) just so i could buy an e6300. hope i get a good one
(each and every one overclocks differently)
good luck with that though, seems like a well balanced system, and remember, and upgrade in the video card will make all the difference for games!
also, if you want the highest quality in games, i suggest 2gb of memory. 1gb will cut it for high quality, or medium quality though.. but it wont cut it for maximum or ultra quality.