I suppose I need to try and borrow someone's power tap for a few rides... just to confirm that my power data is reasonable at least. Or is there any way to do a proper calibration (hanging weights etc) with vectors?
As for smoothing algorithms, I have no idea what strava does to the data once it's uploaded. To get the data I go to his ride, then select the segment for the entire course and click "export effort as virtual partner" and choose the .tcx format. My data is directly imported into GC from the original .FIT file.