Android, I thought of a way around that.

First, do the test with R1, 2 and 3 on the FOX.
Then do the test with S2, 3 and 4 on the FZR.

Then overlay the Fox's R2 and R3 with the FZR - there will probably be some vertical ratio to make both fit. That ratio can then be used to accurately predict where the R1 graph should be, and will give a meaningful crossover point.

Yeah, I'll probably just test R2 and R3 on optimum temps to note the difference, then move the R1 line accordingly

*bump*
I've now updated the graph with new R1 values, estimated for FZR.

Do you still have the readouts for the fox? I'd like to know wether the maximum R1 temperature on the FOX is different to the estimate here.
85°C seems pretty close, though.
Great work.

Vain

The curve is the same, it's just a bit flatter and more "down" on the scale. Optimum temp (85°C - that's what LFS and my tests say) readout for FOX was averaging on 1.7g, max value 1.72g.

Btw, the FOX values were measured at 105kPa, -2.6° live camber.