12 speed beacons around assemberlers 3 machines creating items needed for Red science packs full with lvl 3 productivity. Actually using 3.2 k iron, calculator says needs 23,000 iron plate per min for 3000 Red science Per min.

Definitely wrong

Using the Creative Mode mod, I built a little factory to make 3.1k red science per minute, using 12 beacons with level 3 speed modules per assembler, and level 3 modules in each assembler.
This required 26 machines making red science and 2 machines making iron gear wheels.
The Max Rate Calculator mod says this requires, Rate: Items per minute
Inputs:
Copper Plate 2590.5
Iron Gears 2590.5
Iron Plate 3840.5

Outputs:
Iron Gears 2688.0 (wiht 0.073 machines surplus)
Red Science 3108.0

The production graph matches these numbers. I don't see how you're seeing that the calculator says 23k iron plate required.

I've added a screenshot to the main mod page (the 5th one), showing this test.