I removed mine for cosmetic reasons and also because we own property with some steep terraces that are know to knock air dams off or break them.
I have a 15 Silverado with a 2" level and a Ranch Hand brush guard on it, I have not seen any difference in my mileage since I took it off several months ago. This photo is before I put my Ridge Grapplers on but it the best pic I have of the front.
In a 275/55-20 like he is looking for, the Falken Wildpeak AT3W is 7 pounds lighter than a BFG All Terrain KO2. The Falken is a 6 ply while the lowest rated tire in the size for KO2 is D, or 8 ply, more plies equals more weight.