Right now im running a 4870 1GB on a 22" LCD samsung monitor and it is amazing. I played Crysis and am now moving on to Crysis:Warhead right now... (Alt+Tabbed to check this forum actually..lol)
I've done a LOT of research on the tests and benchmarks various websites and computer retailers/makers have done and the 4890 is only ahead of the gtx260 and the 4870 1gb by like 4-5 FPS. Of course its better at larger resolutions but with a 22" inch monitor, I believe the max you'll be running at is 1680x1050. That's what mine is atleast and its a very nice res. I'd invest that 80 dollars elsewhere (if that is indeed the actual price difference) on things such as games or what not. I just got my 4870 last friday and its handled everything on high and maximum settings. You will not be dissapointed with a 4870. It's got your back.
You should list all the specs of your computer.. Im thinking about in the next 6 months putting in another 4870 1gb- this could be an option for you if you save that 80$ for a while. I say that not because it isn't sufficient for any game you could possibly throw its way, and not that it can't handle anything on its own- I'm saying that because it is so good (in my opinion) I want to see what two can do
You should list your PSU, motherboard, RAM, Hard Drive and maybe even the case you have. You might not have the other parts capable to upgrade but then again, if you've pinpointed between 4870 and the 90, you should have decent knowledge about which parts go with what. Im not trying to advertise here, but I went out on a limb, changing my mind from the GTX 260 to the 4870 and Im happy. I would have been happy with a GTX 260, but I'm overly satisfied with what I have.