Should I use a hard pad with an ultralight mouse?

No — a smooth hard pad with a 45g mouse causes overshooting because low weight and near-zero static friction make the mouse keep moving after you stop. Cloth pads offer controlled glide with more dynamic friction, letting you stop precisely and make planted micro-adjustments. For a sub-50g mouse in an FPS, a medium-texture cloth pad like an Artisan Zero or G-SR-SE is the safer bet.