So I was painting my neighbor's house the other day but I was getting really frustrated because my frame rate was dropping to like 20fps which is ridiculous! (I expect real life to run at at least 60fps).  So I went into my settings and fiddled around with my video options and I found what was the bottleneck for my GPU.  All I had to do was turn down my "Shadow Quality" and now my real life runs like butter.  So if you don't mind some low resolution shadows, you can make your real life run great too!