I chose the 650 over the 610, here's why
The 650 has barametic altimeter and compass, the 610 does not. The 650 comes with rechargeable battery standard. The 650 is able to broadcast 5watts over GMRS, compared to 2watts. Those were my main reasons, I didn't find the additional memory and photo capability of the 655T valuable to me. I've loaded some free maps from gpsfiledepot.com and also converted some pdf trail maps and uploaded them to the device. I picked up my 650 on amazon for about $350. I also got the PTT earbud & mic, which I will post a review for. I will be using the cheapo bike mount kit from garmin, with nylon ties on to my semi-rigid mountain strap on an M8.
Truth be told i really debated the usefulness of the radio/tracking at all, and for that matter, the Montana has a larger screen for less money (I think).