One of my favorite boots is the Sidi Crossfire. Part of the reason is the ease of changing the soles with the SRS system. My current boots are ready for new soles. In this video I show how to do it.
Sidi Crossfire 2 Boots
Sidi SRS Sole
Sidi SRS Enduro Sole
For extreme conditions I have had good luck using the Sidi enduro sole. One thing to keep in mind is that the boot does not release from the footpeg quite as easy.