Isn't it amazing the variety of views one can have about the pace of music! What one person finds sedate others find too fast for proper articulation.
I must say I am on the fast side of the question and found most of the performance very good. The choir, I thought, was excellent (look at the famous or at least familiar people standing there - surely many of the 16 were present?), and on my equipment there was no hint of slurring. In fact, I thought the opening Kyrie should have been quicker yet - it is such a trudge if it isn't taken with some speed.
If anything, the orchestra was on the large side, but the sound was wonderful. The violins played beautifully with lustrous tone (in baroque terms). I don't think I've heard lovelier sound from HIPP violins anywhere else. But that is obviously only my experience.
Actually I was watching it on BBC4, and the sound there is certainly better than on Radio 3, whatever format.