[urq] S6 tune - what % effect on mpg?

[Seán Mac Cann]

I have a stock 1995 5-cylinder S6.  It's my daily driver.  I've found
a good engine guy who can do a sensible tune of 320bhp / 500NM.  I'd
have no issues with this guy's work quality; my question is would
tuning it like that ruin mpg (for a daily driver)?  Fuel prices in
Europe (where I am) are bad.  If you do a tune like that, would you
increase fuel consumption so much that realistically it becomes a
weekend car?  Or would masses of torque and a good remap mean there
wouldn't be much difference in normal driving?  Thanks.

Sean