Hi Ladybird,
Welcome to the board.
I'm 5ft 2 ish & I've got a 620 monster, I can get both feet down on the floor, not quite flat but nearly. You should be OK depending on the inside leg with any of the Monsters upto the 1000 as they all are around 770 seat height.
Best suggestion I could make get round a dealer and try them, the other thing you'll find is that the 'pre-loved' bikes are usually lower then brand new so that could make a difference.
Enjoy,
Dawn
