I like the motor suggestion but to allow for a couple or three climbs and still have a good reserve power I think I'd want more like a 1500mah 3S pack for this big and heavy a model.
The website with info says 68 oz or 1930 gms flying weight for the model. So we'd want around 400 to 450 watts for a sporty climb of around 30 seconds to get to 300 to 350 ft. But at 450 watts off a 3S pack the current is 38'ish amps. And that means a full power run time from the 850mah of 0.85/38 x 60min/hr= only 1.4 minutes or a bit less of full throttle run time to LVC. That's pretty shy even for only one climb up to altitude if not flying in a contest. I'd suggest that for sport flying where you want to climb up two or three times or catch a thermal on the first climb and don't want to change the battery after landing from the one climb that a 1500 to 2200 might be a nicer option. 2200 is likely overkill but I think a good 1500mah pack would be a nice "three climb and still soar for an hour" option.
Another motor option which is in stock is
THIS SUPPO MOTOR OPTION . The Dr Kiwi notes in the link on that page suggests a 12x6, 12x7 or 12x8 might fit with this motor nicely for what you're doing. Or their
LEOPARD LC3536-8T looks like a similar weight and performance on a 12x6 or 12x7.