I can take the performance hit - it is hardly noticeable anyway. But why do you say it is a invitation for bugs?
Some stuff is well used, well tested and important to implementors. Other stuff isn’t, and may work for you but there will be some crappy card out there somewhere that will screw it up. You learn to avoid these problem areas and to some degree code to the lowest common denominator.
Persistent backbuffers smells to me like one of those areas you don’t want to rely on.
I suggest you do this.
Implement it your way (or a similar simple test), then readback the second frontbuffer after swap & check the results.
If it matches your expectations within the bounds of a diff, then do it the fast way. Otherwise, do a readpixels/swapbuffers/drawpixels, on the backbuffer, as a fallback and let that hardware take the hit. If they don’t fix their drivers your app will be a little bit less optimal on their card.