Steve,
To the best of my knowledge the 2610 and 2620 are identical to each other save that the 2610 uses a memory card (that can be removed) and the 2620 has a built in form of "HD."
I went with the 2610 because when I told the sales person (at a store that sells nothing but GPS stuff) that I wanted to be able to fuss with my routings on my computer and then upload to the Garmin the routing I was satisfied with, she said go with the 2610, that I'd be frustrated with the 2620.
As I said previously, I am quite satisfied with my 2610.
Ciao,
Doug