I've owned both the Oregon ATC9K and the GoPro Hero HD. Forget about the Oregon, GoPro is the way to go. Can't speak about the other models, like Contour etc...
The new LCD add-on for the GoPro is very small, it doesn't make it "clumsy" at all.
Here is a GoPro User forum I found very useful:
GoProUser.freeforums.org • Index page