I believe that could be your main problem. 250 mm/s could be your default travel speed. What slicer are you using? Check all your speeds (travel speed, wall speed, infill speed, etc.)

In slicer you set desired max speed, but you are limited with accelerations and actual size of the model (distance). Printing speed will never be higher than speed you have set, but it can and it will be lower most of the time, depending what are you printing. So if you set 1000 mm/s it will not print that cube any faster. Printer needs some length and time to accelerate to max speed, then slow down before next corner.

Anyway its bad idea to push speed limits while having other issues, leave that for later. In my opinion, 20-30 mm/s is slow printing, 40-70 mm/s normal speed and 80+ fast printing. 100+ is almost impossible for most printers without losing a lot on quality. Check voron, they can push 150 mm/s easy, some even go above 200. Printing faster than 150 mm/s is available for well dialed printers and experienced users. My 2500$ ultimaker barely can do that and failure risk is much higher.

My advice, set speeds at ~60 mm/s or even lower (travel speed 150 mm/s). Find best temps and settings for your filament, try to get desired quality. Try higher speeds after that.

You didnt answer have you dried your filament. PETG tends to soak a lot of moisture and its almost mandatory to have filament drier.

For PETG you dont need higher speeds than PLA for sure. You need higher temps, better dialed retraction and dry filament. If you want to increase speed, you should increase temp accordingly.

If you are unhappy with your max speed, consider switching to 0.6 or 0.8 nozzle. If you need more help its best to provide all information you have (printer model, speeds, temps, filament, any upgrades on printer, etc) to make it easier for everyone.