comparing the hqprop 5.1x3.1x3 popo with my favourite hqprop 5x4.3x3 v1s.
first impressions: the 5.1x3.1x3 is stiffer, has similar speed (just my feeling, not measured yet) and takes a bit more amps (158.5a vs 152.2a in these particular flights and also seen in other flights).
but see yourself.