there isnt a lot of difference between the two cards. if anything, the 460se might be slightly faster........ if you have $200 to spend you should be able to get a LOT better card than the gtx550. You could get a 6950 or gtx560 for that moneys.
Both will OC pretty well and even then they won't hold a candle to the 6950.
The only question I have is if your PSU is adequate. If you don't want to do a bunch of research, I suggest you stick to Antec, Corsair, Seasonic, or XFX. You'll want a 500W for a single card and a 650W or more for dual graphics.