The .307 and .356 Winchesters are both listed as 60,000PSI CIP factory ctgs, same as the .308, on the chart I have.
http://kwk.us/pressures.html

One could get better than .30/30 ballistics with the .307 - but how much better? I think I'd rather go with a straightened .220 Swift case. Better rim and about the same capacity or a bit more. Will have to check - sometime.