Potential new room, will this work well?

Chadnliz,

Careful with how you make it 8' smaller, you could be right on or very close to two dimensions sharing integer multiples. That means you will have some very large reinforcement modes at the frequencies where they overlap (or come close to overlapping) room mode wise, like I do where my room shares integer multiples (18' width and 9' ceiling).

You might find this helpful, since you can still make the room any dimensions you want (lucky you...):

http://www.acoustics.salford.ac.uk/acoustics_info/room_sizing/?content=best

Chadnliz, pay attention to Jkalman's advice. If you shorten the 40' dimension by 8', you end up with 32', depending on exact wall placement. Then you would have dimensions of 32 and 24, all divisible by 2, 4, and 8. This would not be good for mode distribution. If this leaves you confused, suggest you search archives on AudiogoN and Audio Asylum. Lots of information is available on this subject.