I'd been telling myself my old i3 clone was simply slow, the way you accept a thing because changing it sounds like effort. It ran Marlin, it printed fine at 50mm/s, and anything faster turned every sharp corner into a row of ghostly echoes. So I kept it at 50 and grumbled.
This weekend I finally flashed the board into bridge mode and moved the actual motion planning onto a Raspberry Pi running Klipper. The setup is more fiddly than flashing a single firmware: you describe the whole machine in one printer.cfg, and the Pi does the heavy maths while the board just drives steppers. The first print after that was uneventful, which is the right kind of result.
The real change was input shaper. You stick an accelerometer on the toolhead, run a resonance test, and Klipper measures the exact frequencies at which your gantry rings like a bell. Then it pre-distorts the motion to cancel them. Mine resonated around 38Hz on X and a bit higher on Y, which explained the ghosting perfectly.
With that calibrated I crept the speed up, expecting it to fall apart. It didn't. I'm now printing the same parts at 120mm/s with corners cleaner than the old 50mm/s output, because the resonance that limited me was never really about going slow. It was about not exciting the frame. The printer didn't get new hardware. It got told the truth about its own physics, and suddenly it flew.