I've been kinda lucky as I don't have great ventilation 'yet' (working on it) because of the time of year/weather. That's beginning to change and last week we had a few unseasonably warm days, around 65F at night, where the temps hovered around 82-84. That's changed for now and I figure I have time to finish harvest (One plant in the 4th week of flower ATM) before I start to have more serious trouble as we get into Spring and things warm up.
I'm new to growing but I am a fast study and I've done a fairly good job educating myself thusfar I think. I've only seen problems up in the mid eighties when the light is within a certain range. I've got a 400W HPS on her so if I am say within 10-16 inches and the temps rise above 80 for too long that seems to be the limit for the leaves which I've seen then burn or simply curl overnight on the tips and edges. Raising the light helps that some, but the plant still slows down a lot after a while of that, combined with the loss of Lumens increasing exponentially with the distance it just hurts all around.
So anyhow, what I've gathered is the general consensus is that if one were to absolutely have to pin down a 'best temp', most seem to say 78F.
That said, I also understand there to be an 'exception' of sorts to that, where higher temperatures can be preferable, up to as much as 85F in fact, however 'only' with the addition of CO2 levels well above the nomal levels expected. Normal levels being 300-400 PPM and the elevated levels being in excess of 1200 PPM, or 'at least' 3 to 4 times higher. Levels of CO2 at or beyond 2000 PPM, however, are generally considered the 'burn' point for plants.
REF:
http://tinyurl.com/cuqcga
I'll bet this is old hat to 90-95% of those here from the knowledge I've seen around these parts, so sorry for the history lesson for all the old hat guys.