Will your cab support a 12? If so, try it. I would think a larger driver would give a bigger sound. In theory it seems like it would.

BUT... If your cab can support one, meaning, the driver wont be too big for it, I personally wouldn't cut the baffle circle any bigger. At least not until you know you're satisfied with the results. If you cut the baffle's circle larger, then you may not be able to bolt your old 10 back on.