Keep in mind that the 4850 has a single-slot cooler that exhausts hot air into
your case whereas the 9800GTX/GTX+ both have a double-slot cooler that exhausts out of
your case. Since most of the reviews show this cooler to be woefully inadequate (a la the 8800GT), it would probably be wise to wait until DAAMIT's board partners start shipping 4850s with their own non-reference double-slot coolers.
It also looks like DAAMIT has finally overcome the dismal AA performance of the 29xx and 38xx series. This is going to be a very interesting summer.