Chris, unless you have the bigger tank for it already in hand, or it is a very arre species that wont be availble when you are looking to upgrade, dont get it.
One of the most ridiculous comments I hear in this hobby is "planning an upgrade". That is the biggest crock. SO often, you'll hear, "I just bought this beauty 12" naso for my 55 gallon. I know its too big right now, but Im planning an upgrade to an 8000 gallon, so I'll be fine". Well, then wait til you have your 8000 gallon, and dont buy the fish. Nasos will still be around in a year ior two or ten when this is running. But, more than likely, your "upgrade plan" will be delayed extnsively, if not cancelled. And all the while, the fish WILL suffer.