Hugh is like a poor man's version of David when it comes to those high notes. Alec got high falsettos that even Jon can't nail after SWW(correct if I'm wrong). As far as my memory goes, Richie can also sustain long and high notes but on a lower octave to Jon's. Same goes to David too but on a higher octave compared to Richie. Jon had a huge range and if you want to know it then watch the video above