It'll generally be a speed increase - but not necessarily "this diameter brush will now move at an acceptable rate" kind of thing. Things will definitely move faster, and you can handle some larger file sizes better, but there will still be things you'll need to wait for a couple of seconds - like your large Smudge brushes, Gaussian Blurs, Radial Blurs, etc. Again, algorithms too complicated to be an instant redraw on the screen.