on the road, I use a heat dissipating rotor like Shimano RT800, but so far on gravel I've been perfectly fine with the stock rotors, whatever they are.
I put my money into good hubs and rims, knowing full well whatever I use is going to get the snot beat out of it, ridden hard & put up wet. On gravel I actually try to brake as little as possible on gravel as speed is so hard to come by. I probably brake way too much on twisty descents, but have friends who can barrel down the same road with hardly touching the levers. I tend to finish well behind them.