For those who want to buy overpants, my advice would be to buy pants designed to be overpants rather than buying a larger size of a standard fit pant. Learn from my mistake.
My pant size is 30 inch waist and 30 inch inseam. I bought Fieldsheer Highland riding pants. According to the Fieldsheer sizing chart, I would fit a size small (30in waist/31.5 in inseam). Since I wanted to use them as overpants, I bought a medium (32in waist/32.5 in inseam). The fit was not ideal. The waist is too large so the pants sag and force the knee pads to sit a little too low. While sitting on my bike, I find myself pulling up my pant legs to get the knee pads in to a comfortable position. The legs taper and can be difficult to snap close over my boots. After nearly three months of use, I have had enough.
For Xmas, I bought myself some Aerostich Darien pants. They're expensive for textiles but appear to be of very high quality; goretex; taped seams and stitching. While researching the Dariens, I did not come across one negative comment. I love the full zip sides. I won't have to struggle to squeeze my boots through the pant legs. Since they fit right, they look more like regular pants. The Dariens are plain looking which I like. Hopefully the Power Ranger comments by children will stop.