Port flow and at what lift does it go flat is the determining factor for valve lift. Kind of wasting expensive heads that will flow high numbers up to 0.700" lift. Conversely using a cam that provides that lift with heads that peak at about 0.500"lift is pointless. If the heads peak at 0.500" valve lift, then a cam that provides a max lift of 0.530" will allow a few degrees more time at that flow rate. Considering that higher lift requires stronger springs to maintain valve control, and those springs create higher friction in the engine. A few thousandths will not create exponentially high loading.