Never used my Grendel on deer but found 123 grain amax far better than 123 grain scenar due to the amax being designed for the grendal throat. Hornady are now making a 123 SST so if you can get them I would think these would work very well in a grendal as they would be making them for the American AR15 6.5 hunters.
I have two friends here that use AR-15's for deer hunting . Both have custom made uppers . Ones in 6.8 SPC and the others in 6.5 Grendel . Both have made some very nice shots on deer out to about 250 yards with no problems . And these were shots on whitetail deer , so I would assume if they did okay on whitetails Roe should be a snap !