The GTX means goretex. Supposedly keeps water out (apart from the big hole where your foot goes in!) but also lets (some but not all) moisture out.Over a long run, you will accumulate more moisture on the inside than the membrane can cope with - think boil in the bag!
The other roclites e.g. 295, 315 are not too bad and probably the best in the inov-8 range for combined road/trail,
I'd also look at more cushioned shoes for ultras such as Mizuno Ascends or Salomons. I'm no expert on those but I'm sure someone else will advise.......
