Lots of unknowns here, but if you like the hard physical contact and you want to make a career out it, you could go a long way as a number 8, if running and tackling is your thing mid-field center. For many big guys fitness will be your biggest hurdle. Good luck!
i reckon flanker open side (number 7) will suit you the most :D
For your size, if you are able to run 40 yards in 4.7 seconds that's incredible (I find it a bit hard to believe to be honest, but I'm going to go with it anyway). But anyway, you would almost definitely be used in the centres (probably ourside centre) or left wing. It depends how could your handling is. If you are good at passing and catching, centre, if not, wing.