Yes, the G2 is a really, really good unit. Personally, I think you'd land more comfortably within the 60-80% of labeled peak capacity zone by using a 1000w unit, which would help to extend the life of the PSU, the noise level you'd regularly be having with the unit under demanding load situations and also the clear headroom you'd have for any spikes or unexpected fluctuations on any of the rails, but based strictly off average from the wall capacity needs the 850w unit would meet the necessity of the configuration and the G2 is a unit that can actually meet or exceed it's rated capacity and expectations.
If any 850w unit can do the job, then that one can. Any issues you might experience won't be likely to come as a result of that units quality or workmanship.
There IS however the factor of electrical deterioration on all electronic components that sit for long periods of time whether they are in use or not. This is commonly known as metal whiskering and capacitor degradation. You can find information on this with a simple Google search but suffice to say that pretty high quality components were used in that unit and it is unlikely you will have any problems for a long time. Hopefully you also registered that unit or have evidence of your proof of purchase from when you bought it so that in the event you DO have any issues with it, you can get the warranty honored.