I think there's a very noticeable difference – but you don't have to take my word for it, because lots of research has been done on this subject. For example, see Vazquez-Landaverde, P., Torres, J. & Qian, M. (2006) Quantification of trace volatile sulfur compounds in milk by solid-phase microextraction and gas chromatography-pulsed flame photometric detection, Journal of Dairy Science 89, 2919–2927 – or just search for 'uht milk taste' on Google Scholar.