Interesting thread about temps =)
I swear I have been debating forever about colder temps and humidity with my peers forever despite proving my point.
What I have found in my instance, colder temps are generally more beneficial in many ways and outweigh the positives.
I live in an extremely warm & humid climate, so I run an A/C cooled room at 20C for entire operation (clone, veg and flower... even drying)
*The res stays at 20C - no root issues
*Plants grow at the same speed as higher temps
I use a good 20L per day dehumidifier and keep RH at around 25-30%. It makes things a bit harder with low temps (stripping water from the air), but with a good dehumidifier and good circulation it's not a problem. The benefits with end production of buds vs happier veg/growing temps, the buds are much better colder (and yield)
The rooms are divided by light, but the air circulation is the same all round. I spray the clones with 'stop wilt' instead of doming them, works much better for me, better success.
The advice I would offer for anybody wanting to run a colder room, just keep the RH as low as you can, keep the fan blowing around really well and in my case (but not necessary) use a UV-C light in your grow room. Yes they are dangerous if used incorrectly, so if you were thinking about using one, RESEARCH and put your SAFETY FIRST!
But in the final 3-4 weeks of flowering I give all the plants a 'scan' with the light every second day and never ever have a bud rot or PM issue since. I use overalls, gloves and a UV face mask. ( I don't let the light touch my skin)
Even just putting one deep in your intake will do good things, but like I said RESEARCH and SAFETY FIRST!
Sorry if it feels like I pulled off topic a little bit, but the relevance was that when I originally dropped the temps, humidity issues and related diseases increased. But if you can control them, you will end up swearing by lower temps like me =)
Cheers Jimmy.