I find a set of clip on ND15's cut in ~half (at the point where the glareshield meets the sky in the usual ACFT I fly) and clipped to a spectacle frame (even if 0 dioptre lenses) gives the best all round performance.
In VMC, my eyes are protected from the outside glare but I can still see the instruments clearly and when flying IFR in and out of cloud, where it can fluctuate one minute from dead dark to bloody glary (when skimming along through tops) my eyes are still protected and I can still see the instruments despite the fluctuating glare and darkness without putting sunnies on and off. And you can easily flip the clip ons up when you're before the the minima when in poor viz to actually see your landing point!
Ordinary sunnies render it fairly difficult to see some non-backlit LCD displays -especially polarised lenses.
You have to hunt around for an optometrist that stocks non polarised clip-ons or will order them in - they're quite cheap. The set-up works well but looks bloody dorky, though - don't forget to put on a "proper" pair of cool looking sunnies once on the ground!!
