The panniers won't fit, as Tim said, but the top box should fit - although I haven't tried to fit a 1200 Vario topbox to an 800's topbox plate, but I believe it will fit. I have a Vario topbox from a 1200 fitted occasionally to my F800GS, but it's mounted to an adaptor plate from an R1200GS.
As for the panniers, it's not just the exhaust cutout, I believe the mounts are quite different too.