Ya, I wouldn't get too carried away sizing those cast bullets down... a cast bullet and a jacketed bullet act very different in the bore. As an experiment, sure, and I can see the utility of that. I would also abandon IMR4064 and just stick with IMR3031.
I run .309" bullets in both my 336 and Savage 99 (.308WIN) and they work pretty well, but I was prepared to go to .310" if I needed to.