Well.. I solved the lag issues (that definitely can show up) by doing certain changes in preferences... by default, I'd get some lag, too. But configuring things in a certain way, Photo is flawless for painting. Brushes with a higher number for the distance between samples, no line smoothing, no wet edges, and of traditional media, mostly the standard brushes from the app, the default ones, which are typically fast.... I believe helped, among several other things, deactivating OpenCL. Turns out it is detrimental for painting, for some reason... and I believe also configuring Windows INK deactivated for my wacom's specific profile for Photo (I have an Intuos 4). "High Precision" in Photo's preferences, and some other things changed there (I have it all in my notes, lol, can't remember right now). Photo (v2) allows one to paint smoothly even on an Adobe RGB, 16-bit file of large dimensions and several layers, and using reasonably big brushes (if all is configured in a certain way in preferences and the wacom utility).
Kudos for two things...: Keeping an Intuos 1 (I keep one on a shelf, due to nostalgia) and mostly, using oil pastels. I was always more about actual oil paints, but those are great, too. Let alone a 3B pencil (and really anything between 2B and 6B). I had a passion for Staedtler pencils (particularly 2B).