Which card in which camera?

I've been shooting with a 32GB SanDisk Ultra in my 80D without any issues. I just purchased a used G1X and thinking that I had a 16GB card in the 80D I picked up a 16GB SanDisk Extreme thinking that I would put the Ultra in the G1X and the Extreme in the 80D.

There doesn't seem to be much of a speed difference between the two (90 mb/s for the Extreme and 80 for the Ultra).

Would you you put the bigger/slightly slower card in the 80D or G1X?

As far as the speed factor, it probably makes little if any difference which card goes where. In light of camera image size, I would use the largest card in the 24 mp 80D. The G1X is 14 mp.

That's pretty much what I was thinking.

Sandisk extreme on a faster higher demand camera for sure.

I mentioned this many times. Sandisk Ultra, especially older Ultra, is actually not a fast card at all. It "transfer" at 80MB/s, but that is the read speed. Ultra's sustained write speed is at 11-12MB/s, just enough to meet class 10. Sandisk Extreme will read at 95MB/s and write at 45-60MB/s depend on which version you have. No comparison in both speed and quality of the card.

I would likely use the bigger card on the camera with bigger files but I would also run a test on your 80D. Hit the shutter on continuous and shoot until it slows down to sputtering. Then time how long it takes to clear the buffer. If there is not much difference, put the bigger card in it. If there is a big difference, you will need to decide how often it will be a problem. If you don't shoot continuous much, it may not matter at all.

I would also be willing to swap the bigger card into the G1X when that is the only camera I'm taking for the day and I want to be sure I have enough space.

You don't need to be stuck with just one configuration.