The maximum bed temperature for PEI is determined more by the way the PEI is adhered to or deposited onto the metal plate.
For PEI sheets attached with the 3M adhesive, I found that at higher (ABS -at 105 C / °C, ASA -at 100 C °C) temperatures, the PEI eventually starts to detach and form bubbles, which determine the highest temperature.
The PEI powder coating has the potential to deal with higher temperatures better because the fusing anand baking process used for powder coating is normally a better bond.
Keep in mind with higher bed temperatures, you have to keep the enclosure temperature high as well to avoid a steep temperature gradient from the bed to ambient internal temperatures. Temperature gradients result in differential contraction ratios which result in warping. This is why much higher bed temperatures are probably not needed unless you are printing very high temperature-temperature filaments e.g., PEEK.