I don’t know that this has really attracted the interest of typologists, though I’m happy to be corrected. The phonologist I used to work for as a research assistant was considering writing an article, comparing the speed of newcasts, but I don’t think he went ahead with it.
I think the impression we have that Spanish is faster than Swiss German is real; but Roger Hughes is quite right that there will be extensive variation, not just between speakers, but also between registers, genres, and emotions. It’d be averageable, and measurable especially within the same genre (which is why my boss wanted to use newscasts). But I haven’t noticed it becoming a thing with linguists.
The real distinction linguists make, as Roger also points out, is syllable-timed vs stress-timed languages, which is a phonological, not a quantifiable phonetic attribute. That one actually surfaces a lot here on Quora.