This is the million-dollar question. The 5S has a faster CPU (Rockchip RK3588), but the optimizes the specific hardware of the 3S (Rockchip RK3328).
While recent firmware updates for the aim to improve performance, they are primarily "maintenance" updates for aging hardware. For users on older versions, a major mid-2025 update significantly improved app stability and interface responsiveness. However, the evpad 3s latest firmware update better