Raimey,
OK, you more or less answered my questions. I glean from your answers that Bertram likely doesn't anneal and trim their cases to length prior to shipping. There is no way a proper 6.5x70R case could stretch to 74.5mm in the first sizing. When making some of my own cases I depend on the stretching and would be happy with half that much. Bertram cases are expensive enough to buy but your experience with cracks in their new cases means the actual cost for useable cases is much higher. You asked why RWS would sell Berdan primed cases, I don't know if they do, but if so, it would be to use "on hand" production equipment rather than setting up expensive new facilities for a few cases. Your procedure for annealing with the water in a pie plate is pretty much what I was suggesting. You might find it convenient to have one of your boys to tip the cases over while you wield the torch if you are annealing a batch of cases rather than individual ones. Trimming 74.5 mm cases to length by hand takes a lot of time and effort, it would help a lot if you saw most of it off first. I use a horizontal/vertical band saw, but it is hard to get a straight cut. I think a small (3or4") cut off saw from Harbor Freight would be a better choice if you don't need something for general machine shop work (and cheaper too). The $100 per round ammo is collector ammo, not shooting ammo. There is no way a shooter that needs multiple rounds can compete with a collector that needs only one (I'm also a collector and have to be satisfied with a fired case instead of that price). As far as turned cases are concerned, I explored them for some of my other projects and decided against them because the grain structure of turned brass is not as appropriate as drawn brass. The only way it would work at all for my projects was because they were large enough to have very thick walls and 6.5x70R cases would have very little space for powder. As far as the load you found, it seems to be pretty much like the factory load (except with a cast bullet). The other good news is, if the cast bullets (.266") prove unsatisfactory, your larger diameter barrel will take American standard 6.5mm nominal bullets without having to resize them as I have to do with my German barrels. You may need a lighter spitzer bullet to avoid exceeding the length of the original factory bullet, but that would allow a little higher velocity.
Mike