New bike question

hey all, this is probably only my 2nd or 3rd post but I read the site daily, great info and apprecaite reading all the good advice. Right now i ride a Specialize roubaix (aluminum frame w/ carbon forks, clip on aero bars and easton aero aluminum wheels). In Mooseman olympic distance, failry hilly I averaged 20 mph on the bike. I plan on upgrading to something real nice in about a year or two (dont have the money now, but will keep saving until I can get something real nice like a P3C w/ Zipp wheels, hopefully a zipp disc in the rear). My question is, how many mph do you think i would gain w/ just the new bike and rims, training remaing the same. if i did the course today on my roubaix, and tomorrow on the P3C, w/ real nice race wheels, could I expect a free (minus the thousands of dollars I spent) 1 mph gain. go from 20 to 21 just on an upgrade of the bike and wheels??? More than one mph???