The Asus Radeon HD 7770 GHz has its core clock at 1000 MHz and memory clock at 4.5 Ghz.
The sapphire hd7770 ghz oc has the core clock at 1100 MHz and memory at 5 ghz.
Both are 128 bit. Meaning the sapphire ghz oc runs faster.
the 7870 has the same speed as my 7770 ghz oc. But it has 1gb more memory and 2 fans, thus costing 70$ more.