I know I should have come back before but I've been here today for another purpose.
I just wanted to say that, touch wood for luck, I've had P3D running well with GSX installed for some time, so it's unlikely GSX was ever responsible for my ApphangB1 crashes.
If anyone does suffer from these, try turning FXAA off, or at least making quite sure you have the related settings correct in the P3D Display Image & Texture Quality boxes and in nVidia Profile Inspector set up properly as per the Avsim Guide. Remember you will have to re-do your nVidia profile every time yo apply a graphics driver update.
I have a 3840x2160 monitor so I don't really need to use FXAA and I haven't had an ApphangB1 since I turned it off. I may be entirely wrong, but give it a try.