Assuming you're using a 79mm crank, 100mm pistons put your cc up to 2484 (from 2457cc). 30cc is probably of questionable benefit. It will also mean SLIGHTLY heavier pistons (being bigger) which will add to the rotational mass - again a marginal increase - although forged pistons may well be lighter than stock anyway.
A larger bore will thin your cylinder walls which might lead to problems at MEGA high boost, but at more "sensible levels", 0.5mm is really neither here nor there.
I guess the issues are:
1 If you NEED a rebore due to cylinder damage/ big ring gap etc, and:
2 If you want more cc
If you just need a rebore, you'll need the slightly larger piston. If you're after a significant hike in displacement, 0.5mm is probably a waste of time.
If you're getting a new block, forged 99.5mm pistons will do you fine.