Not a straight answer to what you're asking but with TA Specialites rings you can mix and match any combo you like? The forged praxis rings will probably last you longer though
Di2 or mechanical? I've had some issues with Praxis rings and Di2 shifters, for reasons I don't understand at all, while I've never had any problems with Rotor rings. Personally, I'd go for Rotor.
NoQ vs. Praxis
http://www.wiggle.co.uk/rotor-noq-chainring-outer/
vs.
https://www.sjscycles.co.uk/chainrings/black-4636-praxis-works-cyclocross-110mm-bcd-5-arm-double-chainring-set/
Which would you buy for Rotor w/ P2M looking to lower the gearing for road use?