I have a tent a little bigger than yours and I agree with drownomatic, I have a 4 inch ac infinity but I only need to put it on setting 2 or 3 and thats enough. I do have a carbon filter though and some tight bends in my ducting,so your setting may even need to be at 1 or 2 if you don't have a filter.
If you email ac infinity and ask about the cfm for each setting,they should send you the list.