Like PE I've tried C41 processing at lower temps and could never make it work. When I was developing colour I always used Kodak Flexicolor chemicals but I doubt that there is any magic ingredient in Tetenal any other brand that would improve the result. To prove the point to my own satisfaction I once shot four identical films under studio conditions using colour targets as the subject and had one processed by a pro lab, another at the local Kodak 1 hour lab and I developed the other 2 - one at 37degC and the other at 24degC, both in Flexicolor. Can't remember the timing I was using for the 24deg process but I recall it was long and based on a consensus of advice gleaned from various sources at the time (mainly magazines) and seemed to produce correct overall density with negs that looked OK.
I learnt a lot about neg development from the experiment because not only did I establish that the negs developed at 24deg contained a virtually uncorrectable cyan cast but also that the standard of my processing even at 37deg fell a bit short of both the lab processed films - printable but lacking their neutrality and clean colours. There was very little difference between the dip and dunk pro lab result and the 1 hour lab down the street.
The experiment caused me to get a Jobo machine for film processing. After much trial and error I was able to get results pretty much identical to a lab but I always re-ran the comparison test at least half yearly until I stopped processing colour film a few years ago.

OzJohn