Certainly getting this thing together-good work!
Sounds like you're still climbing then..
As for the P&G i feel that such a small lump is probably so small as to be almost inconsequential in its consumption?
A good thing to do is to plot out what each tank would have cost at the published MPG figures, then work out what you saved..
That gives you an idea of what you can write off as "modding money" for the car
My iS with no mods has still spanked through £2300 inc purchase/roadtax parts and fuel in the last 9000 miles and 7 months the fuel would have been nearly £250 more