Operation wise... You will not find $.10 difference in the 2. I'd expect the 8612 to have a even faster processor in it.
I'm not a fan of touchscreen units. In a bouncing boat [Like ours are] it's extreamly easy to hit the wrong thing.... Then have to back out of that and start again..... All The while trying to operate the boat and taking your eyes off where you are going.
Unfortionitly the industery is heading that way.
THIS is the unit I steer people to... You will notice it has knobs....Knobs are your friend.