Spitfire makes only 300 mph?

The spit 2a should have a Merlin XII which ran at 9 lbs/ sq.in without boost cut-out. I believe that no plane would be fitted with a boost indicator that even doesn't show the nominal max boost. Currently the clock only shows 8 with boost cut-out. Also you have to have boost cut-out to exceed 6.2 lbs /sq.in

I think this is a bit strange. I think our Spit 2a is no Spit 2a but a Spit 1a with small modifications.