Hi,
the small guy with 50 kg would win the race!
If we talk about such exercises it is very important to look on the undergound. In an ideal case the mass is completly unimportant. The mass fall out and so it don't cares. 100 kg, 150 kg, 2000kg, no matter. But it is not ideal. We have friction and becaus of that the friction force is directed against the motion. If you look now to wintersports, the mass could be useful, because it melts the ice and snow and the friction coefficient becomes better, but on a street is more mass not good.
[math]\vec{F}_{r} = \mu \vec{F}_{n} = \mu m \vec{g} \cos(\alpha)[/math] This trem slows the fatter guy down and the surface of the street wouldn't melt for a better friction coeffizient.
greetings