There are two variations of both cards:
- The GTX 260 and the GTX 260 Core 216
- The HD 4870 512MB and the HD 4870 1GB
HD 4870 512MB = GTX 260
HD 4870 1GB > GTX 260
HD 4870 512MB < GTX 260 Core 216
As for the HD 4870 1GB and the GTX 260 Core 216, that's for you to decide, here are a couple of reviews:
Those reviews aren't actually reviewing the 260 and the 4870, but they are included in the benches. I always try to find the latest reviews so that we can see the performance from the latest drivers rather than at the card's release 10 months ago.