If you can get the 6-port to a 9000 rpm limit, it will depend on how much greater the driveline losses are. I know with a torque converter they will always be more than an MT. But hopefully you will find out for us!

Just remember that you'll want to set aside enough to cover a new tranny, just in case. Not sure what the 6-speed costs. Awhile back while doing some FI investigations, Mazmart was willing to sell me a used 4-speed automatic for about 1200. But that was awhile back, not sure what it would go for now. And I'm sure the 6-speed automatic would be more.