A few weeks back I was looking at the same two models you are. I ended up going a different route with the Zumo 450.
1. It's designed for motorcycles (it's waterproof).
2. Comes with a RAM handlebar mount.
3. Uses the much cheaper SD cards. It is HCSD compatible. HC stands for "High Capacity", my 8gb card was only $34.00
4. Screen size and resolution is comparable to th 276c.
5. Display is color.
6. Has touch screen controls that are large for gloved hands.
7. Will play mp3 music through my Collett headset.
8. Store and display photos.
9. Has a large online community of users to help learn to use and customize.
10. Can be used in car or truck with a standard RAM mount.
I've used mine in -11deg with no issues, love it and would highly recommend.
http://www.hardcoresledder.com/forums/inde...howtopic=310116http://www.zumoforums.com/http://www.newegg.com/Product/Product.aspx...N82E16858108049