When I listen to some of my rider friends talk about RWGPS elevation gains and then claim that RWGPS must be underestimating, I feel like I'm listening to fishermen talk about their catches.
I just pulled up 3 of my longer rides that are in both RWGPS and Strava:
300K (this past weekend) RWGPS = 6,204, Strava = 4,403 (I never needed my granny gear)
200K (Iowa) RWGPS = 6,623, Strava = 6,046 (some serious climbs as the route went over to the Mississippi river)
300K (Iowa) RWGPS = 7,671, Strava = 5,588 (Not as many serious climbs as the 200K in Iowa and the middle 50+ miles were on the Root River Trail which was fairly flat)
I don't pay much attention to the reported gains. Instead I consider how many times I had to be in my granny gear, if the climbs were more than a mile in length, and if I had to walk up any of them. In addition, I have an inclinometer (basically a little bubble level) on my bike so have a good idea how steep a climb really is.