Just repeated my test from yesterday, with similar results: Temperature 3 C, 38 F. Repeatedly ascending at max rate and noting speed and voltage/charge percentage. Here are my results:
65%-98% battery remaining: 10-11 MPH vertical ascent
50%-64% battery remaining: 7-8 MPH vertical ascent
30-50% battery remaining: 5-6 MPH vertical ascent
I haven't done a lot of horizontal speed tests BUT I did do a few runs when it was around the 50% level and max speed was 30-32 MPH and seemed to take longer to reach that speed.
Definitely seems like a hobbled bird now, especially on the lower half of the battery. Thinking about downgrading.