I don't think they're getting more violent over time. The Regenerations of River and The Master were both pretty similar to the ones of 9-10 and 10-11. The only difference with 10-11 was that because he'd been holding it in to long it was extra violent when it happened and the poor console room boar the brunt of it. I think it also had something to do with the radiation he had absorbed being released.
Also I think the whole Master scream was more down to him being eeevvviiillll!
Always sounds kinda like a bird of prey (as in actual bird not a Klingon ship!!) to me.