So I’m giving this its own post, as I want to keep the main Hero Equipment page mostly about the available sets, certainly with all the new sets added to the game. Below is a chart with the percentages bonus each of the currently 4 Tiers of equipment bonus do, from level 1 to level 10.
The four Tiers (marked *1-*4 in KABAM emails) start out at 1%, 2%, 4% and 8% bonus respectively, but can grow to considerable amounts if you happen to be lucky enough to get gear at level 10! Use this as a reference for determining end-game gear specs, or whatever you like :). Thanks to QuietschEnte for confirming the numbers!