N4P not hitting printing speeds of 250mm/s

What print speed is the N4P actually capable of to properly print quality parts? Because I am starting to think it is unable of printing larger parts at those speeds (where its actually able to reach those speeds) Everytime i try to print something faster than 120mm/s big infill top&bottoms are quite underextruded (to the point you can easily see the layer underneath). The gears are also skipping if printing higher then 200

These are my settings right now:

Material: Elegoo rapid pla+ Speed: 50mm/s first layer 120mm/s overall Printing temp: 215c Bed temp: 65c first layer 60 for the rest Enclosure: yes but open when printing pla

Here's what I tried so far:

1. Increased spanner tension on the pla
2. Decreased spool roller resistance
3. Up the printing temp: caused way more oozing with smaller bits & prints
4. Added heat resistant thermal paste to the nozzle (specially made for 3d printing)
5. Changed the hotend also the little ptfe tube (no effect)
6. Upped the extruder motor amperage in the cfg file
7. . Changed the entire print head to see if the extruder motor was worn
8. Had a failing extruder cable harness so swapped that as well