Gas mileage question


Just wondering to what degree performance mods change gas mileage...

I have a Silver and Black 05 (100% stock)... I normally get between 36-37 in the city..  between 45-47 highway (conservative riding.. )

Eventually, I want to go with a 4-1 full exhaust and PCIII usb.  I'd like to know other riders have experienced after adding similar mods...

I havent gotten a road trip in yet but since i've installed a full Akro exhaust system and a PCIII i have noticed no change in my city mileage... depending on how i ride my mileage is between 28 - 34 city and 45 - 50 hwy... I'm taking a short trip labor day weekend and i'll get to see how it does on the hwy then.
I have 16/42 sprockets, Full Yoshi Exhaust, Pair Block offs, ATRE, PC mapped, and a speedohealer. i generally get around 33-35 city, and 38-42 highway
I have a 4 into 1 Hindle, TRE, PC3 and I am getting 46-48 highway riding semi conservative. Thats dropping down 2 gears for a pass verse 3 and sometimes only dropping one gear. Mine is an 04.