As I said, the trick is just working up the loads to function and be safe. Might even be fun.
Yessir, working up loads can be 'interesting'. There is very little current load data available except the information shared on the internet by individuals. That type data must be approached very carefully, because it, if accurate at all, is certainly limited to the owner, his rifle, and his specifics. I personally chose to limit my loads to the lower/middle range of the 9X57 velocity spectrum and even bought a chronograph to help me from getting too close to the red line.
You obviously have been at this longer and in more detail than I have. It certainly seems as though you have had a lot of 'fun' getting your rifles to shoot. I suspect you have enjoyed the journey as much as I have. I may yet stumble across an original 9X57 and get to work out the kinks sometimes encountered with them. Those long, slender, light, 'between the wars' sporters are a true delight. My build is just a pore boy version of one.
I was unaware that Walther made .356" bores. Can't say it would have made a difference with my build, because I was on a budget and really didn't want to deal with issues one would have added. Anyway, as I said, what's .002" among friends.....