A few extra thoughts have occured to me!
[1] I read somewhere that 'bents are faster than uprights until the gradient exceeds about 7% due to superior aerodynamics, and uprights are faster once the gradient exceeds about 10% due less weight / being better climbers. Not sure whether those numbers are actually accurate, but the principle makes some sense to me.
[2] I've also read that hills on an upright can be fun (if you're so inclined), but on a recumbent they're just something you have to get over.
[3] I had my first successful go on my own little
"Alpe d'Huez" with my recumbent bike today. My best time with my, 8.25kg, roadbike is about 14 minutes 30 seconds. With my 14kg recumbent I managed it in a whisker under 17 minutes. Now one data point is not a Phd thesis, but I thought I'd share it anyway!