I swapped my printer from Marlin to Klipper at the weekend and the same machine, with the same motors and the same frame, is now genuinely faster. Not a bit faster. Properly faster, with cleaner corners at speeds that used to produce a vibrating mess.
The trick is that Klipper moves the heavy maths off the printer's little 8-bit board and onto a Raspberry Pi. The board still drives the steppers, but the Pi does the motion planning, so it can look much further ahead and run things the original chip simply hadn't the cycles for. The board was never the limit on what the mechanics could do. It was the limit on how cleverly you could ask them to do it.
Pressure advance was the big one. It compensates for the lag in filament pressure when the nozzle starts and stops, and it's the difference between blobby corners and crisp ones. Input shaping helps too, cancelling out the ringing you get when a fast move excites a resonance in the frame.
Configuration is a text file rather than a recompile, which I love. Change a value, restart the firmware, test, repeat, no toolchain. The same hardware, suddenly flying. I should have done this months ago.