ive seen a HUGE growth difference when I run my ultrasonic fogger system vs not running it. while running, I can dial in my rh damn near spot on to the vdp chart. 75% rh and 84* temps with it on, 50%rh and 84* off no matter what the conditions outside (I grow in a basement setting). im currently 2 weeks from flip with this run and the veg growth looks 2 weeks behind from not keeping my rh in check. back to having my ultrasonic fogger system running, albeit at the cost of running a 1k lamp for 18/6.
as far as co2, why not borrow or buy a ppm meter and see what the ambient ppm levels are at your elevation. then adjust for there. I used to grow in 380ppm for 4 yrs with excellent results. now I run 1000ppm from flip to harvest and seen a huge increase in yield.