I just bought a Montana 650t, it is to replace my Oregon 450t that I seem to have misplaced (also known as lost). I would agree the t is not necessary if using the chips, but it was actually cheaper than the standard 650. It is bigger than the Oregon, and a bit heavier, but I think the additional screen size is worth it for me. I was very pleased with my Oregon 450, and would certainly purchase another one, I just decided to go for the bigger screen this time.
--Jim