I think they are made incompatible by newer drivers as you have noticed. Windows handled it well for you, but for me and Keltari it blue screens when mixing new (Kepler) and obsolete (Tesla) with current drivers. You also are mixing variations of Kepler and Tesla.
So in a mix system like this it's safer to select the older model card on he driver download page; worst case booting into low-res mode or using a restore point.
I don't see how you can get away with running the newer display drivers.