HI ...
allow me to say something about what U wanted to know... I am a member of the group but yes I have not attempted the GMAT yet ... ceratinly U would not get the actual 'feel' of the TEST through me but as for the rest I can certainly help U ....
fact one: gmat does have math and yes it does have math that 'differs'' from lets say the GRE math ...nice that U are good at verbal that is very necessary.
fact two: GMAT MATH IS IN A WAY tougher , one my friends has opined so ( he has takn the GRE) but thats not what matters rather the way U approach the Math matters... U SEE THE MATH HERE IS MORE A TEST OF ONE'S thinking and ability to work smart than one's mathematical skills... I may not know the (a+b)^2 formula but If i I can know how to insert numbers given from the answer choice may be I have a chance.... hope U understand what I m trying to get at ...
fact #3 : ''top scorers'' ? well there are quite many here.. and so are the future top scorers ... and that s why they all get here to get what they aim for... a top score! how much time ????? well honestly that to a lot extent depends On U ...well and ur ability of course !
statistics and experiences by many say around two to three months at around 3-4 hrs a day... If U can 'pump' more of hrs good for U ..of course U have to use those hrs intelligenlty...otherwise there is no set TIME FRAME ...
I hope I have helped to an extent for I know for a starter nothing is satisfying I was there in that position long time ago

just in case U want to bother me

Please do so I will try my best to help U help urself get clear on this ...
take care...
HAVE FUN