Florida and Arizona both won national titles as #5 seeds.
?
Florida won the NC in 2006 as a #3 seed. They were actually seeded behind a fairly talent-barren #2 seed OSU in a region where Villanova was the #1, and Georgetown was a dangerous #7 who actually played Florida closer than anyone in that tournament (and the Hoyas made the F4 the next season with their future NBA guys Hibbert and Green returning). They also win in 2007 as a #1.
But it isn't all that unreasonable to pick a #3 seed to win the NC. They just should be a #3 seed that you feel has at least one legit NBA guy. UConn won it all in 2011 as a #3 seed, with Kemba Walker leading the way. Syracuse did it as a #3 with Melo. UM with Glen Rice in '89.
Arizona won it all as a #4 seed in '97, and #4 seeds have clearly not had as much success at winning the NC as #3 seeds in the modern tourney era, but at least one of the #4s have been able to make the F4 each of the past 2 years. But '97 Arizona is the only #4 to win it in the 64+ team era. Since the 64+ team tourney started in the mid-80s, on average a #4 makes the F4 roughly once every 3 years. None of the #5s have won the tourney in the 64+ team era.
So to list the #5s and #4s to make the F4 since the expansion in the '80s:
#5: MSU '10, Butler '10, MSU '05, IU '02, UF '00, Miss St '96
(as an aside, props to Georgia and Miss St on avoiding being one of the several SEC schools with zero F4 appearances, a list which grew by 2 with Mizzou and A&M being added)
#4: UL '12, UK '11, LSU '06, UL '05, AZ '97, OSU '99, Cuse '96, OK St '95, UC '92, Ark '90, GT '90
So just starting with 1990 to pick a year, you've had 23 tournaments, six #5 seeds in the F4 and 11 #4 seeds. You wouldn't think there would be that kind of difference between 4 and 5 seeds in terms of F4 appearances, but it is real. I just came up with these stats browsing through the list on the following website (put your cursor over the team name and it says the seed - very easy to review quickly):
http://www.allbrackets.com/
