My '93 WRX when I bought it maxed at 0.6 bar. Eventually found a leak under the IC. Fixed that, and got a much smoother 0.75 max.
Went for a blast yesterday, and notices a max of 0.8. I've fitted an induction kit with cold air supply (tut tut, I know..), but that's the only change.
I understand why cold weather benefits a turbo engine, but would it actually increase the boost pressure? If so, would this indicate why I never get the 0.9 max? The IC does look a bit of a mess - I tried to straighten some fins the other day.

Can anyone calculate / guestimate the bhp drop from 0.1 bar? I did a 14.4 1/4 a few weeks ago, totally wragging the car, which is I believe the book figure for a later UK car with 215 (?) bhp, so I'm guessing it's around there.