Actually 35 mm. converts to 1.38", or about 1 3/8", not 1 5/16". However, maybe you are saying that, although it is marked 35 mm., it actually measures out to 1 5/16", which is actually a little over 33 mm. This may seem like mere pedantry, but for my size and build, it is important. An actual 35 mm., or 1 3/8", is just too wide. I tend to prefer 1 1/8" or 1 1/4", although might go as high as 1 5/16", but absolutely no wider. For a casual belt, wider may be OK, but not for dress (or, in my case, for casual either). Jonathan, I'd consider changing the width of your belts to 1 1/4". BTW, will you have them eventually in other textures (like scotch grain)? And other colors (like burgundy)?
I really like the interchangeable-buckles feature. I try to have a wide range of colors in my belts, and all have been altered to have interchangeable buckles. I have some very nice 1 1/8" and 1 1/4" (and 1 3/16"--or 30 mm.) dress buckles in both silver- and gold-finish. With this setup, I can go with either metal color and the right belt color for all of my outfits. I haven't gone the sterling silver or solid gold route because of the expense, but have found some silver-tone buckles that are the right shape and rodium plated. A less-expensive approach to the system I've gone to--than the sterling, solid gold one--would be to have the brass buckles silver-plated and gold-plated. The former, in particular, is quite inexpensive, but, like sterling, does pose the problem of tarnishing.