With the size of the rider considered, bigger is better as long as he is a competent rider.
Here is something else to consider, I assume that crank has 10 years on it as well.
If this is the case you really need to carefully inspect the crank.
I don't mean wiggling on the wrist pin end and saying "Oh that's good".
Find out what the side play is with a feeler gauge and check against the specs.
If you go with a big bore, you will be exerting more torque on your crank.
If it's marginal it won't last long which is why my 250+ lb employee smoked his crank....
Thankfully it didn't explode on him and blow the cases or it would have been parted out