Quite likely this is caused by the process of polling the video mode list at GM's startup. Two things are known to make this process slow:
- Having a mode list that's too long (this is why super resolutions are helpful).
- Having two or more displays enabled (this usually is what makes the first condition matter, since it requires each video mode to be checked for compatibility with each display, increasing exponentially the required time).
In the end this points to a fail of design of the Windows OS, that we need to bypass with some tricks.
Probably, when testing with your other card, your display setup was a bit different so the issue didn't happen.