Meanwhile I tried out the dual heater mod like others have posted about. I used 2x Bambu 48W heaters for 96W on V2 CHT hotends. I put the extra heater opposite of the thermistor, so the heaters are 90° from each other (the shape of the hotend makes it harder to put the extra heater opposite of the original one). Tried a speed test with 0.4 nozzle using Bambu PLA, it ran fine all the way to the 72 mm³/s limit. Then I did the same with the 0.6 nozzle, same thing. And finally the 0.8 nozzle as well, still no problems. Pretty cool.
I could confirm that if you try to go over 72 mm³/s or 500 mm/s, the printer will silently cap the speeds according to its limits and lower the other speed accordingly so not over/under extruding. So it might look like you’re doing 80 mm³/s or 600 mm/s but you are not. I could also confirm that Ludicrous mode does not change this. When I already ran at 72 mm³/s and activated Sport or Ludicrous mode, nothing changed - it just kept on printing at 72.
So 500 mm/s XY (F30000) and 30 mm/s E (F1800, which corresponds to 72 mm³/s regardless of nozzle) are the limits, enforced by the firmware.
BTW I tried running the same speed tower with unmodified OEM hotends (all sizes) and same filament, just for reference. The 0.4/0.6/0.8 could all do about 30 mm³/s before falling apart. I posted a separate thread about my findings for the 0.2 nozzle.
I haven’t tested stock hotends with dual heaters (yet). Actually I also never tried the V2 CHT hotends with just a normal single heater, lol. Perhaps later but I probably wont bother.
I’ll probably be using the 96W CHT 0.4 for all my printing for a while, with all and any filament profiles set to a max. flow of 72.