I'll bow to people with better knowledge, (Darren, SteveP and Stu) but to the best of my knowlege, a "B" unit running the latest firmware should give exactly the same functionality as a later "C" unit. Indeed, a "B" unit upgraded actually reports itself as a "C" unit.
The only proviso, is that 2010 "C" units are starting to come with LED screens (rather than the previous LCD technology). I understand from Darren and the likes, the screen is a little sharper and brighter, and these can ONLY come on a "C" unit.