the n516 and n517 (7800gt CO SE, and 7800GT CO, respectively)
$300 and $320
so theres no extra cost, and yes it is worth it... better cooling, and its actually a faster card period
my card runs exceptionally cool (about 35ºC idle, maybe 50ºC under load, not sure though)
depends what you'd like: are you going to be doing serious oc'ing?
if so, you'll be replacing that hsf with something like a silencer or vf700cu, so just get whichever is cheaper.
if you aren't planning on oc'ing that hard, but would still like to squeeze a little extra out of the card, get the copper hsf.
the n516 is 460/100, the n517 is 470/100
i believe though, the n516 is supposed to be 460/1050
either way, after attempting to overclock and deciding to settle back to stock, my n516 is now at 470/1100 lol
maybe a frame or two difference in performance, if that