Hi. I use menzerna polishes with Rupes 21, 5" plate and 5.5" lake country pads. I use Rupes pads on Flex 3401 (run smoother than on Rupes itself! and accept pressure added when using 3401).
I also may use Menzerna polishes with rupes pads, however, to date, I've only tested SF4000 on rupes yellow pad and Rupes 21, both 6" and 7" pads.
My camera died last week, so I'm only left with Cell phone poor pics. I hope they can at least illustrate Rupes 21 use with 7" yellow pad and Menzerna SF4000.
Side By Side:
Rupes yellow 6" pad runs VERY smooth on Flex 3401 4 3/8 backing plate:
Here you can see (barely with this horrible pic!) both tools, each one equipped with different sized backing plates, different pads, but same SF4000:
I was working on a Land Rover Freelander2, it should be at show&shine if not for my camera issue.
The after pictures represents areas where I used rupes 21 and yellow rupes pads paired with SF4000:
Before:
After:
This tail light was corrected using Rupes 21, 5" plate, 5.5" white LC pad and SF4000 (few passes, ANY pressure). No stalling on curved light.
Before:
After:
This is a general view of car. Fenders, upper and lower parts of doors, pillars and bumpers were polished using Flex 3401, 4" plate, 4" and 5" pads. The remaining flat parts were polished using Rupes 21, 5" and 6" plate, 5.5"-7" pads. All work conducted using SF4000.
Regarding your will of using the Blue pad and FG400, sure I'd recommend a test spot, but in Advance I may say it'll be extremely aggressive combination.
A tip for working the Menzerna on Rupes: slow arm speed, plenty of pad rotation all the time. I've used basically speed 5 on the above work.
Please, let me know if you need some more info.
Kind Regards.