You will have more even wear if you run them as 32-34 with a normal load. Overinflating them will cause the tyre to wear in the middle.

If you have snow or ice, you may want to lower the pressure slightly to get more rubber in contact with the road, or as the story goes to get under a very low bridge.

I am planning to swap my tyres over every 3000 miles or so to even out the wear (if they are non uni-directional). Must remember to check that.....