The 9800 GT tha the OP listed isn't $100.00 with rebate, it's $119.00 and there is no rebate.  If you want to compare cheapest prices then you need to select and HD4850 with a better rebate as well.

The HD 4850 will last you longer as games get more complex and take advantage of DX10.1 and Shader Model 4.1.

Go for the Radeon HD4850. You will not regret it.

I think you wont regret going with any of them, still I would also go with the HD4850.

so which card will allow 60+ FPS in DMC4 when paired with this processor: http://www.newegg.com/Product/Product.aspx?Item=N82E16819116072

Either, depending on resolution and settings.

assuming the typical 1680x1050, both. even at 1920x1200, both, even without dropping quality.

HD4850 is comfortably above 60fps @ 1920x1200, even with 4xAA and 16xAF
http://www.elitebastards.com/cms/index.php?option=com_content&task=view&id=594&Itemid=27&limit=1&limitstart=7

Even the sub $100 HD 4830 should run at about 60fps at 1920x1200. The 4830 can be bought for about $100 if you need it now and is pretty comparable with the 9800gt (benchmark link follows)

http://www.elitebastards.com/cms/index.php?option=com_content&task=view&id=627&Itemid=27&limit=1&limitstart=7

Without referencing the benchmarks, I can tell you right now that the 4850 will score higher than the 9800gt. It all depends upon what price premium you'll be paying for that bump in speed.

Best bet may just be to wait for the best deal on a 4850.

err what about with a resolution of 1024 X 768?

Both cards will completely pwn that resolution and you will not notice any difference between the two.

If that is your gmaing resolution and you don't foresee buying a new monitor anytime in the next year or two, then get the HD 4670.  All the others are overkill at that res.

actually its 1280X1024, but would those cards still be Overkill?

 Most definitely.