KC8QVO, General rule for rough riding conditions are more air volume, less air pressure. How much air pressure will be determined by the load and tire size.

35 mm, for me, has been a pretty versatile size. I recently swapped to 32 mm tires on my regular T bike and maybe less desirable for rough riding, but if they are, I expect the difference to be slight. My recent back-up T bike build has 37 mm tires and looks to be at the least as good as the 35 mm tires. More experience on either tire could've answered you question better, I know.

Brad