I know you wanted a controller's opinion but I think you'll find that the majority of published minimum climb gradients are for airspace, noise and other such reasons but not terrain considerations. The published gradients are for all engines operating and if you can't make these gradients you will have to reduce your TOW. But all bets are off N-1 when you should follow your aircraft's T/L tables. Although 13% is significantly greater than a normal SID, most modern twins should be achieve this to 3,000'.
PM