At 3" of lift on my truck the back brake line was as tight as a guitar string...You could probably get away with 1" but I personally wouldnt go any higher because if you offroad when your axle droops thats one inch less you have of brake line...I dunno if that makes any sense, but it made sense in my head...Why dont you just buy the longer lines so you can lift it as high as you want?

1999 Black TRD Prerunner X-Cab V6
3 Revtek Lift
32x11.50 BFG AT
8"x2.5" Sway Away remote resi. coilovers and Total Chaos upper arms sitting in the garage begging to be installed