I second that, about doesn't matter. That said, Star is considered to be very good and so is Fed...Winchester and Rem are OK too. The original spec for the .357 was a 158 at 1,500. You won't find anything like that being loaded or in any manual...btw, that was in an N Frame.
The problem w/nickle brass is well known. .357 brass is sorta hard to come by, but .38 brass is disposable...You find it everywhere and it lasts a long time.
I've seen, but never shot reloaded .38 wadcutter in mixed brass. Supposedly, the dif in impact is un-noticeable...at 50 yards. IOW, I suppose that it can be proved, but you'll need a ransom rest in order to prove it. Just like the theory that a .38 is more accurate in a .38, vs in a .357...but I've seen .38 ammo shot in a .357 can shoot 10 shot gps, in the area of 1 1/4 inches...yep the accuracy really stinks.