It is actually possible to have too big of a skimmer. There are plenty of threads about it. The general consensus how I understood it, is an oversized one won't operate consistently. The amount of gunk needed for proper foam production on an oversized skimmer isn't enough and it won't skim properly. This of course has to do with bio load and everything else. Since the OP already has it, I would by all means use it, and adjust a couple months down the road depending on how it acts with the current setup.