Just conducted the Flow Test with the MK5 with MK2 (Plus) spring.
I always conduct the Flow Tests at 600psi tank pressure ( worse case scenario).
Starting with a static IP of 140psi, at 5 SCFM the dynamic IP dropped to 128psi, at 7,5 SCFM to 126psi, and stayed there also at 10 SCFM and finally 12,5 SCFM.
That means that at depth equivalents of 120-200-300 and 380 feet the MK5 with the MK2 spring maintains a dynamic IP of at least 126psi, which is completely acceptable.
I checked some more old MK2 springs, most of them produced a static IP of a bit more than 150psi (152-156psi), one had only 148psi, so it seems to depend on the condition.
Interesting the whole thing anyway.........