I got an Oregon 450T because it was on a huge sale, actually cheaper than the 450. I have been extremely pleased. The touchscreen works with gloves on (unlike the iPhone), I can add topo maps along with Birdseye satellite images to the same sd card, and it made it through 2 rainstorms without a hitch. I actually lost it while blood tracking a deer through some extremely thick brush. Found it a week later (extremely lucky), after 2 big rainstorms with the screen facing up. There was water pooled on the screen. Opened up the battery compartment and after seeing no water, it turned on like nothing had ever happened.
Having said all of that, if money was not an issue I would get the Montana. You can add the City Navigator software and it works just like their Nuvi series in your vehicle. I believe it even gives spoken directions. For viewing on your dashboard I think the larger screen is important. Lots of options out there, but for what I do I am sold on Garmin.