Al, Ben, et al,
I assume you guys are aware, but for everyone else...
GM-800 is a 24vdc radio
....and is mostly a M-801GMDSS with new software
, and new user interface (w/ color display and speaker built-in to control head)...
A nice radio...but, in my opinion, it's not really an HF radio
for most sailors....being pricey and running only on 24vdc, it's Icom's competition to Furuno's, Sailor's, and JRC's commercial
GMDSS / SOLAS compliment MF/HF-DSC-SSB radios...
While the M-802 is getting a bit "old-tech", except for the software
and user-interface, the GM800 (and Sailor's 6300 series and Furuno's FS-1575/2575, etc.) isn't really 2018-state-of-the-art, either.
Also, while we don't know how much longer the M-802 will be in production, it is now....and suspect it will be for the next 3 years (hopefully more?)
So, while the GM-800 is a nice rig, it's not really designed as a replacement for the M-802..