The 255/50 16 R888 is what I ran on the rear of P2 for a long time. We did have to run a wheel spacer with the 16x8 RPF1. The tires are wide enough that they get into the strut tube. They are also kind of tall which is why I didn't go with them again (I went with 225/45R16 but 245/45R16 is better based on your horsepower goals).
I was under the impression that the R888 isn't on backorder and is instead being discontinued. It would be nice if they don't discontinue them because I like that tire.
Here are two places that claim to still have the 245/45R16 in stock:
Tire Crawler R888
Discounted Wheel Warehouse R888