This video is part of the project Early Music Sources with this episode being dedicated to the interpretation of high clefs (also called chiavette) and transposition. There are footnotes in the project’s web page with further references to this video.
Personally, as an editor of sacred vocal polypho, I have found a lot of works that use this clef combination. The usual clef combination of c1-c2-c4-F4 is also frequent but in Portuguese polyphony several other combinations appear such as the common g2-c2-c3-c4(or F3) and sometimes g2-c1-c2-c3 (for SSAT) and g2-c3-c3-F3. I usually keep the written pitch rather than the 4th or 5th transposition. Sometimes it is not difficult to sing the piece in the written pitch, frequently it sounds more bright than in a much lower pitch. In other cases I only edit the piece a second or a third lower. It is enough to keep the voices in a confortable ambitus and the brightness of the work is kept.
Much musicological and now also performative debate has risen about this, and it’s far from being a peaceful matter since there is no clear and definitive answer to this doubt. I’m a supporter of historical performance but, in this case I don’t see any problem in using any pitch to sing the work if confortable for the voices, since pitch was a relative matter in those times.