The 800HO Ptek is just a spiced up 800HO (knock sensor/erave/tps ect) same old engine with a few bells and whistles.
The 800R Ptek is a completely new engine, the reason they kept Ptek with the 800R is because its an acronym (T=TPS E=Erave K=knock sensor) all of which the 800r has! Except its on a completely new engine w/ water cooled crankcase, monoblock, 3d erave ect.
Anyways, on topic.
I found my 800HO Ptek got awesome milage (15+) trail riding (not granny riding but not bagging on it) and it really didnt get a whole lot worse when i was bagging on it.
Cant say much for the 800R, just picked up my new summit last week and their isnt any snow yet!