Check the for sale section for a used GTX 470, they go for around $180 or less.
I had a single 470 with my Phenom IIs and it performed pretty good, you can't go wrong with a sub $200 card.
If the 465 doesn't unlock they're generally slower than 460s (that can hit 900+ core). Plus they are hotter and louder than 460s.
Edit45: The 550 is slower than the 460.
I would go for the gtx 460 768mb version and never look back, overclock your cpu to 3.6 or higher and get that little 460 up around 900+ and you'll have a great system.Edited by BallaTheFeared - 4/24/11 at 4:09am