47 cm for sure. I am 6' 1", with 33" inseam, and I got a 51cm frame with GX option, and find it the perfect height. If I went up to the 56cm, then I would not be able to touch the ground on both sides with my whole foot.
I'm assuming R&M's website has a typo, as it shows that the 51cm GX frame has a 0.5cm SHORTER standover height, then the 47cm. But when you look at the 56cm, it increases the standover by 1cm over the 47, and 0.5cm over the 51. I think they just transposed the 47 & 51cm's standover numbers. That would make each frame size have a 0.5cm increase in standover height compared to the size below it (using GX numbers).
Besides standover height, having 3cm less reach on the 47cm sounds like it would be about right for someone ~12.5cm shorter then me.