Personally I would keep the dual 6" setup, if you have access to a cheap way to try out a single 8" port then go for it, but you will likely have a drop off in "SPL" in most cases but not all.
However, a single 10" wold be a nice setup and would be very fun to play around with if done properly.
The real issue with flared round ports and output is that there are many different views on it. I don't know to many people that actually agree. Most result to testing and then just use what works best your particular application.