33" tires and 4" will look good- that's what I had before I went up, and I loved it! 31's are too small, and it just won't look too good IMO.
Let me make one suggestion- Keep the setup you have on for a little while. When I first bolted the 38s on mine, I HATED how it looked and was looking for smaller tires almost immediately. Now, a few months later I REALLY like them. The 35's may grow on you.
Here are some 4" and 33 pics-