Simplytire without question for tires in GTA. Best prices and can advise you on what tire to get if you want to maintain drivability and comfort.
Me personally I have moved away from RFT's because of noise/road feel. I now have PSS's and love them. Still slightly noisy, but amazing grip.
As for mileage, that's awesome. If you want the absolute most out of your engine and to keep it health then a walnut blast and diesel purge may help. Check out Leslie in markham or join the FB group BMWTrueNorth and we have lots of vendors.
Enjoy your torque beast
And p.s. If you want more mileage go see the boys at EuroCharged who will tune that beast to make better mileage and more powa!