Thanks for the feedback, that is what I have heard from another as well. You don't see to many folks running 5's outside of backcountry ultra's. At least not that I have seen up here in AK. I figure there has to be a reason for it.There is a speed difference. I've ran 4s and 5s on the same width wheel and have found that over 12mph the 5s start to require a bit more effort. My opinion is if the race is important to you then I suggest getting 4s. If it isn't that important to you then just run the 5s.
The reason is they can't get them, they are expensive, and they only know what they have. It's hard to get rid of a perfectly good tire when even 4s last season after season if you just ride them in the snow (my 5s are on the 3rd season). I don't find that the 5s slow me down for races. I did build up a wheelset for 4s recently, but I've raced extensively on 5s and I gotta say they are pretty great. I've nailed several top 5 finishes in races and I never felt like the tires were holding me back. In fact, I don't know if it's just me, but I feel I can pedal through turns easier on the 5s, where I see a lot of other people coasting.I figure there has to be a reason for it.