The wheels are 170mm, but they are geared after the drill motor gear box. Don't know the size of the cogs off the top of my head.

The Electonize's have 40a burst ratings, so I'm assuming a 20a fuse will have the same sort of life time as the burst.

I think you mentioned changing the relay before. One of them is sticking so it'll be worth changing them anyway.

Do I need to change anything else on the ESC other than the relay? I'm assuming it's just a 'straight' swap.