I GOT A G9 IT IS FUCKING AWESOME! if ur in melbourne i suggest either msy or pcmaniacs, maybe have shops near u if not in melbourne. g9 is like 90 and g15 is 94 . im just waiting on cash for g15. if u arent too picky about the lcd screen razer have a new keyboard out that like $10 more than g15 and the razer lachesis (mouse) is similar to the g9. but i chose g9 as i have never used a razer mouse.
i had a g5, broke 4 months. started losing power lost the receipt, plus bro bought it for me so didnt know where it was from.
g7 - i suggest not. u only have 1 set weight, g5 and g9 is adjustable.
g9 - very confortable not that bid, great pads on the base. awesome adjustable dpi and i got purple led's
i suggest look at forums like i did for my headphones, should be easy to find a great review of each mouse