Don't know of any Scotish fitters, but on my last e53 single turbo X5 i had a Tunit Box (They are from Blackburn / Bolton area) that could be self fit. it took the standard 193bhp up to 230ish and made it livable. The sd that i have now with sin turbos and 286 is the one to have, have no real need (and i am a bit of a speed merchant) for any more power.