Shark remap - doing the maths

As there is a deal on with Shark til Monday, I can get a Stage 1 (320BHP) for £299; bargain! Checked with Privilege and they want another £220 ish for the remaining 9 months of my policy.

The question is....

How much better is the fuel economy if anything? Given that people get 25 MPG ish and I am doing 10K miles per annum - I reckon that's about 400 gallons of fuel a year. An extra 2 MPG will save me 30 gallons a year or about £190 thus justifying the insurance hike in my mind.

What do you reckon?

John