Best vid card for STOCK Q6600

Hello folks,
I have a PC with a Q6600 running stock 2.4ghz with a ASUS P5Q mobo. I have the good ol' 8800GT which has worked great for years. The card is starting to get a bit flaky so I'm looking to upgrade. I'm wondering what is the best card I can get for my system (w/o bottlenecking, etc). I have searched the forums with various suggestions but many say to overclock but for various reasons, I do not wish to overclock. So I'm looking for the recommended card for a Q6600 running at 2.4ghz. I see a lot of 550ti cards cheap but wondering if my CPU at stock is too slow.

Thanks
 
Thanks for the tip. I'll probably stick to my current system for awhile. My hardcore gaming days are over so for my other standard uses, this rig is still pretty good and hope to keep it around for awhile. Just would like to do little upgrade tweaks here and there in hopes that I can run the occasional modern game on at least medium settings with a 1680x1050 display. The 550ti looks like the winner here for me.