New CPU

Hello,
So I have $150 bucks to upgrade my 775 CPU from an ancient Pent.D 840 Extreme Edition. My MB is an ASUS P5ND so it will handle pretty much any 775 CPU - there are a lot of Core2Duo and Core2Quad out there, and depending on where I look, a ton in my price range - any I should be zeroing in on?

Upgrade to c2D/ C2Q for now .. I think not worth, you should keep it. Next if you budget a lot of from now get lga 1155 + SB . Sometime upgrade not worth , alway's follow update of hardware. New and new .. just opinion

I have an EVGA GeForce GTS 250, which is performing quite well, and I am not really a gamer. You really think I should just stick with my old Pent. D? It's draggin down my Win7 score, and I feel it's a bit sluggish. I really have no wiggle room on my $150 - so I can't really start to think about a new 1366 setup - and I don't plan on a wholesale update of my system for a few more years to be honest. I'm stuck with my DDR2 for now - I am running 6GB of it though. I was thinking of picking up a q6600 (slacr) on ebay - based on some of the things I've read - but wanted to know if I should be looking at some Q8xxx or Q9xxx in the same price instead - or even if there was an over performing Duo I should be considering?

Perhaps an inexpensive duo and a better performing HD for the OS? (running 2 250GB HDs they are 5400s (Yikes!))