Upgrade hot-end to achieve higher temps (e.g. for PETG)
Most PETG reacts vey badly to temperatures above 255. The typical optimal PETG temperature ranges from 225 to 245. Above that it gets sticky...

If PETG is your goal, you might want to find a filament that is more friendly to your printer. They are pretty cheap, and now you have transitioned to an all-metal hot end, you should be good to go!