Hi,
I don't think you would see a BUNCH of difference on a 36" hood vs a 48". You will probably notice the very ends of the tank will be a little dimmer, but if you do not plan on stacking rock all the way to the end of the tank and placing coral on it, it really won't make much of a difference. I like the look of tanks that have suspended hoods that are a few inches short on each side. It doesn't make the setup look so "top heavy".