Here is a 66mm whoop frame designed for printing in polycarbonate.
It's taken ages to design something that actually stands up to crashes (this has taken many hits without breaking) and has better flight characteristics than stock Whoop frames, see for yourselfs:
It's far stiffer than stock frames I've tried due to the material (polycarbonate) and the design of the frame with vertical braces holding each motor in place.
This leads to great flight characteristics with no discernible washout.
The price for this great flight characteristics is about an extra 2g of weight over a stock frame (around 5.5g) and you need to be able to print pure PC.
I fly this at 2S so those extra 2g don't really matter - and man this flies great, even with relatively big 2S batteries...