Wowww!  

RE:

1. I Agree ! 😊 

   I just upgraded the MK4 to the FW 5.0.0 RC and I am printing the MMU3 in Prusament PLA.
   This piece is printed in INPUT SHAPE mode, with Variable Layer height, using 0.2 SPEED PrusaSlicer profile, and  will takes 5h:32m.
   Without IS it would have taken  on MK4 9h:43m 😦  And on the MK3/S+ 12h:30m 😱 

   The print is not yet finished, but you can see here the extreme fast of the print:

   POSITIVE:
   Things that I have noticed during the print, is the extreme accuracy of the infill grid (on the printer with KLIPPER I got often the infill grid corrupted and ruined)
   
   NEGATIVE:
   during first layer sometime it missed the last millimetre of filament before a nozzle travel: when it retracted the filament and went away it detached away also a small piece of filament from the plate.

   During the print sometime I heard the nozzle "scratching" the grid infill, but this happened very few time till now. On the KLIPPER printer on the contrary, this happen much more often, and it is almost all the time the cause of a failing print, because the grid become damaged and then the layers drops to do spaghetti.
   I hope it will not happen on the MK4. Till now the grid is perfect.