32x18 works out to a 48" gear. That's mighty low. The fact that you can average such a high speed is very impressive. You must be a great spinner. That's good for long term health. On flat terrain, if I had to choose one ratio, it would be a 66 to 72" gear. I understand you need something lower for climbing, and you made a good choice, but I guess I wouldn't do SS for a hilly area.