40 watts is wayyy too high for realistic gains from aero S5 + wheels. For a joe-average rider who might put out 175 watts in a 60min time trial (or triathlon leg), that would mean a nearly 25% power savings.
Also, the notion that someone mentioned about 4 minutes saved over 48 minutes (10% of race time) is also hugely overstated. Even with ALL the aero toys, you'll be lucky if you even get 2 minutes per hour of racing, and for most folks it'll be closer to 1-1.5mins with all the aero toys. Unless, of course, you're comparing to a fully upright nonracing position, but that's less of an equipment issue than fit issue.
I made significant progress this past season by training a lot (for me at least) on the bike, and raised my FTP by about 20 watts. It was a very noticeable difference - way more than my aero wheelset and aerohelmet combined yield for sure.
Last edited by hhnngg1; 08-11-13 at 11:52 AM.