Why did you limited it to 125 bit range?
Exactly because of what said by TheArchaeologist, 125 bit range is already very large range will require ~1 year on 256 V100.
If you count only the energy, puzzle #110 and #115 was with benefit but #120 is not or you need to get a low cost electricity.
Anyway, the mods to do in order to increase this limit is simple.
Yes, but only a fraction of all adresses have published their pubK... I think it would be best to create an AI for this task.
Even considering this small faction, you will still have more odds to win with a kangaroo or rho program.