I've had adult painteds (which are similar to your sliders, I believe) and they didn't do much re the plants. IF you plant enough oxygenators (anacharis, hornwort, etc)––which adult turtles WILL eat (a good thing), they should multiply faster than your turtles can eat them down. Aquatic turtles are generally herbivorous and sometimes will nip lily pads but I haven't lost many leaves at all. I feed them supplemental turtle sticks (which has all they need for nutrition) and this keeps them happy enough that they leave the fish alone (turtles will eat fish if they can catch them, though the fish are awfully fast compared to a turtle) and munch on your oxygenator type plants before the 'preferred ones'. YMMV, though.
I've heard turtles will eat the roots of water lettuce and hyacinths, but again, mine have not done much damage that way at all. And since both plants reproduce so fast, it's not usually a problem.
Plants I have WITH the turtles; lilies, parrot's feather, water hawthorn, hyacinths, water lettuce, egyptian papyrus, black taro, flag iris, hornwort, pennywort, and horsetail rush. So you can see, lots of choices, and if you plant enough, feed the turtles the sticks, they'll not affect your plants that much, imo.
Michael