I think 125% speed will satisfy noone.
- It's not realistic, so it won't satisfy those that want realism.
- It's not fast enough to increase the frequency of gameplay decision for those looking for a more arcade feeling.
I think listing the game speed on the online game list would work fine. Like that, you could let the host select whichever speed (100%, 200%, or even 50%*), then players could select see this in the game list and jump into those that they are okay playing. Over time some of them will be more popular than others. So what? Everyone is happy.
*Yes, I am not crazy. 50% speed could make sense on a game mode where you would have many other things to do, like aiming and shooting weapons Mad Max style, dropping and avoiding oil pools, throwing dynamite and avoiding it. It would give it a more tactical depth that would be too much at higher or even normal speed. You could even have the game run at normal speed, then automatically slow down, bullet-time-like, when one of this events occur, to give the other players time of reaction. Just throwing some ideas on the table here...