The guy who won Hawaii this year ran a 2:42. The second place finisher at IM Florida (Sergio Marques) also ran about that speed, Sergio has also held the fastest marathon in Hawaii last year. Both of these people also did these runs of really fast bike splits. At an IM, there is NO drafting allowed and there are cheaters. But the run can un-ravel the best triathletes so what does it matter if you are just a runner. Zach Ruble, a 9:06? IM guy ran a 2:58 mary at IM Wisconsin this year, at Florida, he finished in 10:51, a good time for average people, a poor time for a pro. In Ironman, you are dealing with lots of time and lots of variables, in a marathon, you have a bad day and have to take some walk breaks. At an IM, you have a bad day and you are walking a marathon if you are tough enough to not drop out. At Hawaii this year, Rutger Beke (4th place IM Hawaii the year before, winner of Ironman Arizona 2007), blew up and walked his way to an 11 hour finish, this is a sub 8:30 guy who has posted a 2:48 run in Hawaii. These people mentioned are better runners than 98%of people on letsrun.com these people have competed at top levels of Ironman racing.
Now all that being said, some letsrun.com kids think that because they are decent runners that they would clean up IM racing, think again, you need different strengths in different areas, it matters not if you are a 2:30 marathoner if the bike is going to take you 7 or 8 hours (because it will since most runners don't have the strength and power to Time Trial for 112 miles).