I have both 2 ACR and one Mcmurdo. I purchased the Mcmurdo when it was on sale for $200--and for its smaller size. I agree that the ACR 2881 (plus) which floats is the best choice. HOWEVER, just because it floats, it does not mean that the unit does not have to be held in a position, so that the antenna will work properly. The "non floating" PLB can be made to float with a simple "float coat". The advantage of the full size EPRIB, is that they float, in the upright position, so that the antenna is oriented to send the distress signal. All of these are GPS enabled.
I agree that the Standard Horizon radios are excellent. I do not have one with a GPS, but do have a small hand held GPS, with marine charts in my ditch bag should it be needed. I can see the advantage, if you can contact someone with the hand held. Remember that the range under ideal conditions will be 10 miles--but in reality most likely 5 miles or less. Lets say that the radio is one foot off the water--if you are lucky--when you are in the water. Assuming that another boat had an antenna 10 feet hight...that gives you the 5 miles..Yes a 2,000 foot high CG antenna on a TV tower, would have a longer range--but it is very unlikely that you will be within 10 miles of that antenna....
The built in DSC will give some advantage, and is worthwhile. The ICOM IC-M92D also has these features. The SH HX851 does have an additional feature I consider almost essential for a survival radio--you can buy an AA battery tray. I have my strobe, flashlight, GPS and radios (Yeasu VX-8R--2 meter, 80 CM and 6 meter (mod for Marine VHF also), with GPS--as well as 2 Marine VHF portable radios) all use AA batteries as a back up. I carry a dozen extra AA batteries in the ditch bag.