I'd definetly go for the larger unit, because of all the reasons mentioned above. Upgrades in the future, etc... Or, say you have a mishap in the tank, something dies overnight. The larger skimmer will pull more out than the smaller, ofcourse. And you cant really overskim, just set it to skimmate that is more dry.
Which reminds me... I STILL havent set-up my deltec yet, cause I havent set-up the new system
Chris