I would do a little research 1st before you go for triple glazing. 28mm triple glazed units will make very little difference to double glazing, Ideally they should be at least 44mm units and even then the thermal improvements are probably only something you would notice on paper.
A decent thick set of curtails would make more difference or secondary glazing
I agree too, I have triple in my house because of the road noise so I went 6.4 lam, 4mm float and 6mm tough. It's the size difference that stops the noise and like DH says it's only minimal, more muffled than normal and that's it really.