I’ve studied for both the exams and I can give you some insights. I decided to go for GMAT at the end, but it’s your personal decision.
Firstly, GMAT is only for management and business (MBA, MiM, etc). If you’re not sure about your degree and looking for something other than these degrees, then don’t go for GMAT and just go for GRE. However, make this decision first.
Secondly, major distinctions in syllabus are: GMAT quant is slightly harder and goes more in depth. You’re also expected to score higher in GMAT quant.
GRE verbal is focused more on vocabulary whereas GMAT verbal is based on grammar and logic.
I found GMAT verbal to be easier for me as I suck at memorizing vocab and I settled for the gmat quant as it was easier for me to improve my quant than verbal. I ended up scoring 700 Q49 V36. I really didn’t get a chance to study for verbal and regret that but overall I’m content with it.
Essentially I would suggest you read up more on this (many blogs available comparing the 2). See where you stand on verbal and quant and which section will be easier for you to improve. Either ways I believe anyone can improve their scores to 700+ or 325+ with the right amount of efforts.
Also, I do not think many of these conversions are very accurate so take it with a pinch of salt.
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