I am not trying to be an asshole or bash what you are doing(with enough funds, i would like to do it to). But you changed too many variables like gearing, 7.1+l engine, lowered it some more ect; to test the reliability of the new engine with how you had it set up before the changes. The new engine at 3300 rpm should live a long while. The old engine probably would have held up just as well with the gearing and lowering changes. I thought you needed lots of rpms for those massive twins to stay fully spooled(4000+rpms)
Nobody knows what it will take. Last year it melted down at 3800 rpm, far below the power peak of 4400rpm. The high DA does have a major roll. It effectively reduces your turbo size.
The 10% increase in displacement will drop the power peak of the twins 10%, which was 4500. So now the peak will be about 4100. The twins also have a wider powerband than the big single. I can also tighten up the turbine housings.
My guess is we will need to leave it in 5th, but if I can run it in 6th, I will. It's nice to have options. We can also drop the drive tire dia 10% as well, and go 3650rpm in 6th.