I went drag racing!

I would probably look a little closer at timing and distributor curve to see what improvements can be made and then start leaning toward a larger carb. But before that, I would start looking closely at the fuel system. I think you are having a fuel delivery issue causing it to go lean out on the big end. Not saying the aforementioned 750 or 800 cfm carb wouldn't help, but it may be needing more consistent fuel pressure or some jetting and metering rod changes.