8mm was what I was thinking myself, and would be quite sufficient. The only one that really needs a clear view of the lyrics is the singer, after all; but you want them to be able to face the 'audienc' for the most part as well.. hmmm.

Wel, if you spaced out words appropriately- using spaces to alter flow a phrasing- you could get the timing down to the word, and indicate held syllable with repeated letters. o/~ With or without youuuuuu, with or with out youuuuuuu o/~ for a bit of U2 as example. That'd manage close enough for most songs I think.

--Chiaroscuro