Btw imho the worst part about RPi is that it has poor ethernet performance. This improved a bit with RPi 3+, but still meh.
https://openbenchmarking.org/result/1805276-FO-1703199RI52
It's hard to asses a generic ratio, since the performance increase is wildly variable. I think it can be reasonably assessed a "base" 3x performance ratio against the RPi 3B (with an outlier of 8x).
Btw imho the worst part about RPi is that it has poor ethernet performance. This improved a bit with RPi 3+, but still meh.