OK, I did some searching on Swaylock's on this paddling speed subject as it relates to shortboards. I found an absolutely fascinating discussion here:
http://www.swaylocks.com/forum/gforum.cgi?do=post_view_flat;post=260433;page=1;sb=post_latest_reply;so=ASC;mh=25;guest=18905839
Surfers were discussing why some shortboards are faster paddling than others.