I agree with the others Ram 2 more gigs 6 is over kill I have 8 and never go over 4 except on rare moments. You over clock anything? That e8400 can to 3.6 or 3.8 easy and that 450 is just a tweaked up 260gtx non 216 so getting a little old it will overclock nicely also but still very limited. after the ram and a few tweeks you will feel like you have a new computer
I have a similar config (8400 stock, ATI 4870 and 4 gigs of ram running 7 x64.) An SSD would make it feel like you just turbocharged your PC. Although you will see little performance in games besides level loading, It gives your PC a whole new lease on life.
although it's age is starting to show, the e8400 is a damn solid chip, and like some others have said it's pretty easy to squeeze an extra 10-20 percent of juice with some light OCing and an aftermarket air cooler. Even stock cooler should do 5-10, maybe more.
I play a lot of games and it's treated me well for almost 4 years now, even though SB chips have tempted me to update my rig, I don't feel it totally neccessary yet.