Hi there, and welcome to
TestMagic.
You'll probably get a better response about your GRE in the
GRE forum, but I can tell you that you should stick to the material from your test. If you're studying for the GMAT, use GMAT material; if you're studying for the GRE, use GRE material.
There's plenty of good material available, so there's really no reason to shortchange yourself in this respect.
