If you take a 2.0 engine and use all the same parts , turbo , tuner the larger 2.3 / 2.5 engine will always make more TQ
To say airflow means nothing with a turbo is a little silly , air flow means everything , yes turbos are under boost but the more airflow you get to the pistons the more TQ you make the better the airflow the better the TQ
I do agree people get to cought up in HP where they should be talking TQ , TQ is where the money is and show me the money LOL
If I was doing some form of racing I would think of using a 2.0 vs a 2.3 / 2.5 for the rpm factor but in 95 maybe 98% of the time 7000 will do the job nicely and even the 2.5 can turn 7000 in most cases if you cant get it done at 7000 ....another 1500 rpm to 8500 isnt going to help much if any
In all the years and the 1000`s of tuning / dynoing the Focus engines I have seen 1-2 engine make power past 5500 let alone 7000
It goes back to the old saying
"There is no substitute to cubic inches " not even cubic dollars
Tom