Welcome to the conversation, Andy.
🙂
I do not have either of these lenses nor have I used them. So, I will leave it to others to comment about performance. However, I will note that it is interesting to compare the two lens designs on the Voigtlander website at
www.cosina.co.jp. Stephen Gandy at Cameraquest says that the P II has a new optical formula in order to make it more compact, but the differences between the two designs are hardly discernible when looking at the drawings.
I think that the key point in the redesign was to make it more compact because criticism of the original Pancake was that it wasn't amy more compact than the Classic. Even with the redesign, however, is it really more compact? It's not as long as the Classic, but it is wider & heavier. It also uses a bigger hood & once the hood is mounted, the advantage of shorter length is lost as well - unless you opt for the supplemental lens shade for the Classic. In the latter case, it would be worth knowing how important this is vs the smaller hood that accompanies the lens & under what conditions. Confusing, huh?
The Classic would appear to be the cheaper option @ $229. However, if you add the $55 cost of the Voigtlander M-mount adapter, there's not much difference now that the price of the P II has been reduced to $299. You can save a few dollars by substituting the generic M-mount adapter from Stepehn Gandy for $33 - and then there's the question of whether you need to add a $45 lens shade for either or both.
The Classic has received excellent reviews & user reports, so the key difference may be in build quality. Like most of the later Voigtlander lenses, the P II seems to be the better of the two in this regard. Good luck with your choice.
Cheers . . .