My figure was from Strava, so you'll probably finish at a similar rate of climb ( strava has you down at 18,000ft+ @500+ miles) Is strava really that bad at calculating things?
It is at elevation, i find gpsies more accurate, but i use enough to get my data, garmin training centre for raw data, and rwgps because its what i started using for elevation when I had the phone and v.a.m. (i can now work this out myself, well the spreadsheet.) and power, but this changed with the hrm it's almost double that with out one, see for the most part it's all just arbitrary, the main reason I correct elevation is that even the 500 can be out by 60+ ft between gain and loss, so you have to chose one and stick with it, garman connect gives higher gains usually.
I just cant ride as far as you Reece in one ride, you know why.