I'm a three time IMLP finisher. My first time in '03 was like this years race...but colder.
I've used road bikes and a tri bike to do the race. My first year my wheel set was Spynergy deep dish carbon. The last two, Bontrager XXX light on the front and Bontrager Deep dish on the back, both carbon. Both sets were sew ups. (glue ons)
In '03 The Carbon sucked in the rain and wind. Period. Folks with disks were all over the road and there were some crashes due to wind. I volunteered at this years race too and talked to tons of folks on Sunday night and in line on Monday. They said that braking on the carbon in the pouring rain was just horrible especially on the 10k drop into Keene. All of them were VERY thankful it wasn't too windy.
The heavier your bike is at Placid the more difficult it is to drag that stuff up the lumps.( I've ridden the course over a dozen times in training.) Go as light as possible equipment wise then don't load the bike with ump-teen bottles. There are well stocked aid station every 10 miles.
The road surface is actually good. Yes there are a few rough sections, but nothing bad enough to worry about...they do a good job every year of resurfacing where safety is an issue.
In my HMO, I'd go with the HED 60/90.
This year I'll be riding my road bike with Scandium rims on the wheels. After 7 years of riding carbon, I'm going back to metal. The bike still comes in at 16.5 lbs.
See Ya there!