Update -
Tried forcing AH2 onto a single core - it maxes it out.
Running on both cores they both run at about 75%, so going to stick with running on both cores.
Game is smoother, more snappier.
One noticeable change is bringing up the clipboard -
Instead of 'sliding/scrolling' into view, it just appears, real fast.
Frame rates in the air are way way better, even with lots of smoking stuff and flames on the ground still get 50+.
This is with the detail sliders set to about 75%, ground viz at max 3 miles.
Overall - Very very happy.