I think 200 mm is overkill. The Noske Field Scope, a handmade scope made in the '30's, had 6" (150mm) of eye relief and was specifically designed to allow the scope to be mounted in front of the bolt handle on unaltered Mausers and Springfields. I have several of these scopes which I have used extensively on bolt rifles up to and including .577 caliber and I find them ideal.

Maybe I'm mistaken, but trying to align the pupil of my eye even with a relatively large exit pupil (probably no more than 12mm with a 1" straight tube scope) at more than 6" seems a pretty difficult task.

I know that they're unfashionable now, but several of my favorite hunting scopes, including the Noske, have 22mm diameter tubes (Lyman Alaskan, Zeiss and Hensholdt Zielklein) and I find them completely adequate for all but the most extreme hunting conditions. They have the further advantage of being capable of being mounted extremely low, right on the line of sight for iron sights.