Marilyn Sholin (
www.MarilynSholin.com) works at 200-250 ppi. Jeremy Sutton (
http://www.jeremysutton.com/) works at 150 ppi. These are two of the best Painter artists on the planet. At that size you can up-res if necessary and still retain the painterly look.
The original of the attached file is 8" x 10" and 200 ppi and it printed up great. (The mom liked the pseudo-canvas texture, which I believe helped sell the effect. Generally I don't do this.)
If your results are looking too much like a photo, in my experience that's symptomatic of "not enough simplification." You might consider applying blender brushes such as Grainy Blender or Grainy Water to further disguise more of the detail.
I hope this gives you some ideas.
~Danny~