[ Letting go with a mortal will probably never happen. They're too fragile, too easy to break and if he'd ever seriously hurt Ianto beyond bruises and scratches, he's not sure he'd be able to ever play rough again.
The noises spilling out of Ianto serves well to encourage him and he picks up the pace, keeping up the rhythm pretty well so far. Only a matter of time before he falters, really. ]