There is a large difference. GMAT AWA is much eazier than GRE AWA. I have prepared seriously for GRE AWA, but only got 5.0. I haven't prepare GMAT AWA section and got 6.0. GRE topics are too deep for Chinese students. Most of it recquire extensive training in philosophy and history. Liberal Arts background would be at advantage. Generally speaking, if you are confident that your verbal ability is among the best in mainland China, you can demonstrate it through GRE. Getting GRE verbal score of 700 equals 800 in GMAT, assuming you are not math dummy.