Gary, with all due respect, longer fins, such as commonly found on surfstyle boards like XBC, Shred Stixx and Inland Surfer do provide more drive and thus speed. Take two boards of same surface area and the board with properly placed fins of 3"+ length WILL BE faster, will have more drive than the same board with 1" fins. The channeling of water through the fins helps provide lift. Additionally, the greater surface area of the larger (and possibly more fins) gives greater drive forward with less side to side pumping energy.
I would concur that MANY folks think a "board is a board" and so we see 400 pound folks unable to ride the 4'4" Coex - gee I wonder why?
I would also point out that fin depth and the number of fins plays a significant role in the drive and "terminal velocity" of a board