Don't know about the benchmarks but the specs are in order. The R770 is supposed to come in GDDR4 and GDDR5 flavors. There will be a 512MB GDDR4/GDDR5 and a 1GB GDDR5 one that should have a clock speed reaching almost 1GHz.
Could be an early version as GDDR5 was just shipped out earlier this year. I know there will be low end versions with GDDR3 and GDDR2 (I know its old) and the high ends should be GDDR4 and GDDR5.
I agree it looks like it could be fake but its hard to tell as GPU-Z might not be codded to see the info right. But the 4870 is supposed to have 480 Pixel shaders.
But if it is a fake he did a good job with the text. Then again it is supposed to start arriving around end of May early June. Or I hope they keep with their dates.