I am a cat 2 cyclist and am building up a winter bike with spare parts I have laying around (Scott aluminum road bike with apex components and a rival crankset). My bike i train on all summer is a tarmac sl4 with sram red and a quarq power meter. I am debating on getting a stages power meter for my winter bike so I can do endurance rides and other workouts that are low intensity high duration. Is it worth it? Or should I just take a break from power and just ride without it all winter.

used powertap from slowtwitch

Why not just transfer the crank from one bike to the other? It takes like 90 seconds to do that and then you can use that same crank all winter long.

Make sure you don't just do all low intensity, high mileage throughout the winter. You should be getting some good intensity all winter long. It's not 1995 anymore :-)

Because my tarmac has bb30 and my Scott has gxp BB. And I don't want a power tap because I like my wheels

Why not use the Tarmac over winter? Just make sure to stay up on the maintenance if it gets grimy.

Also, there is a pretty solid power thread over in the "racing" forum (it says "just starting...", but there is a wealth of information comparing meters and such):

https://www.bikeforums.net/33-road-bi...ents-here.html

The BB30 Quarq will fit English bottom brackets with a Rotor BB.

if you're doing low intensity then why do you need a power meter?

I think the other potential challenge you face is comparing data from two different power meters. I know that this is highly debatable, but many of the reviews show that the various power meters are perhaps not exactly the same from a consistency stand point (meaning they all read consistently when using one or the other for baseline purposes but that they read differently often enough when compared to each other). I could be wrong though.

I personally use a Stages and have been happy with it from a cost effective crank based option I just don't know that I would use it in addition to a different one if using the data from both as my guide to training. I would probably simply swap or use the tarmac on the trainer