I'm also skeptical that an 80-minute Grande Messe des morts is sped up beyond recognition.
I was considering buying the Chandos disc but this has put me off, may have to hang back until I can sample it.
Sir Colin Davis took a very expansive view of the work - 91 mins in 1969 (recorded in Westminster Cathedral) and 94 mins in 2012 (recorded in St Paul's Cathedral) ; the large venues may have determined his tempi. Bernstein recorded the work in the Chapel of Les Invalides, venue for the first performance, he takes 87 mins. Munch (84 mins) and Fremaux (83 mins) are quicker. I wasn't impressed by Fremaux (live or recorded) though the Agnus Dei in his recording is very beautiful. I haven't listened to the Munch for quite a time, possibly need to refresh my memory.
Davis (1969) was my introduction to the work and for many years it was the only version I owned so he very much colours my view.