The Core 216 gets a bit more performance, giving it the edge on the 4870 1gb and runs cooler if you get the 55nm, uses less power, and if you're RMA-ing anyways shipping isn't too big a factor, and you have $25 evga money that you can't use for anything else? Then go for the upgrade 😛
The difference won't be night and day to you though, keep that in mind. It just gets a bit more of an edge, a few more fps if you will, than your current 260.