Hmmmm, that's like asking how fat will you get if you remap your cakes with more cream and sugar. It depends entirely, as already said, how often you eat the cakes!
For context, my Edition 30 has been Stage 1 most of it's life and the long term average is 28mpg. Daily motorway round trip of 70 miles, mostly at 85-90. Lots of boosting.
If I nannied it everywhere and never exceeded 70mph, I expect it'll be in the low 30s, but I like cake