if you can do well on the MCAT verbal section you should do well on the GMAT verbal section. The sentence correction is different, but studying for that test will give an advantage.
The Physics section on the MCAT is also similar in that it tries to trick you, so all in all I think you can do better than a 550 in a month. 550 is not that hard, especially someone with a testing background in verbal an quant.
You can go to MBA.com and download sample tests that are pretty close to real thing and most people here swear by their accuracy.
That should give a good idea of where you stand.
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