Father Zed is, as always, right. Having looked at that lovely video of the Mass of the Americas, I share his observations that
(1) 'solemn' doesn't have to mean 'It needs to take a long time'; and
(2) liturgical things can happen simultaneously, in a very natural sort of way.
I would myself tentatively add
(3) Processions do not have to happen slowly.
It would certainly be dreadful if everybody, as in Dryden's comment on Ovid's hexameters, went "at the hand-gallop". But processions should go at the normal relaxed but business-like human pace in which people move who are not in a tearing hurry but simply need to get from point A to point B.
Slow processions are so pompously Anglican, so embarrassingly clericalist; so terribly "look at me".
I mean this next bit seriously:
Liturgical organisers should have experience of the Byzantine Rite. Not ... Heaven forbid ... so that they will 'byzantinise', but to help them to understand the distinctions between Solemnity and Pomposity.