Need help with sprocket size and have exhaust question

[jones2507]

I have a 06 busa with full rs-3 yoshi exhaust BMC air filter and Brock's pair valve block offs. Want to know if I keep the front sprocket stock and just go up 2 in the rear will I still have better take off but not lose as much mpg or is there a combo that won't affect mpg as much I don't want to get 20 mpg. Also can I just put a Brock's shorty meg slip on onto my full yoshi good idea or not? Thanks