Comparison of Scores
The GRE has come up with a tool which can be used to compare GMAT and GRE scores and get a decent idea of where you stand in case you want to decide with which score to apply. The tool is old, but will serve the purpose in most cases.
A few of the scores have been presented below. However, this should be good enough to give an idea of the other scores as well (taken from the GRE score conversion tool by ETS).