Sylas didn't feel the change immediately—maybe because it flowed so naturally, or maybe because the UniForm had increased his mental capacities so much that it was hard for him to notice such minor changes to begin with.
But what he did feel was free. There seemed to be no greater control in the world than Runes, and when they flowed around your body, it was like the universe was blessing you in a way—caressing your body and soothing your soul in ways he just couldn't fathom.
If he wanted to, even breathing could be helped. He could filter out oxygen in the air, making it more pure. Or he could change the pressure in his lungs, making the diffusion of oxygen into his blood more efficient. Or he could slow the flow of blood in exact parts of his body so that recovery would be faster and he would benefit from the oxygen more.