The Rain and GTX versions are almost identical. The GTX version, as mandated by Gore, uses top grain leather. The Rains are made with Sidi's proprietary Technomicro synthetic leather which is much like the superb Lorica they use in their cycling shoes. The membrane in the Rain is a taped membrane like that made by eVent or others. I haven't used the GTX version, and agree it's a much nicer than the Rains, but I found the Rains to breath reasonably well. My Sidi Cobra GTX boots are no more breathable.You probably have the Adventure Rains that are plastic and don't breath. With the Goretex I have not had that problem, they seem to breath pretty well.
What I like about the Sidi Adventure boots is the walkability. My offroad exploits are pretty tame. If I wanted more protection I'd probably go with the Sidi Discovery.
To the OP, here's my take on the Rain: Sidi Adventure Rain
Trailsurfer definitely has a valid point about PU coated leather and how it doesn't breath. These are an inexpensive touring boot, but as Trailsurfer would point out, they won't breath well, and to Scott's point, they'll be the minimum of protection for even light offloading: Alpinestars Scout WP I have a couple friends who wore their Scouts from Idaho to Tierra del Fuego and another 7,000 mile around India, so I suppose even the "cheap" boots can get you by.