Humidity Question

So does anyone closely control humidity in their grow room? I have a 7 light room(1000 wt HPS) with CO2 burners(I keep co2 between 1200 and 1300). The AC keeps temperature at 81 f.
In theory the drier the air, the more easily the plants can respire. Or am I missing something here? I just put in a dehumidifier. What is the optimum humidity I should be aiming for?
Any thoughts?

veg you want a bit more humidity(50-60% is ok) and flowering you want it lower around 35-45 %

So the humidity is running around 40, up to 55-60 the day I water. The plants seem happy, maybe drying out a little sooner.
Do other people use dehumidifiers?

Its the dead of winter here, matter of fact -30 windchills today, I have a humidifier, but its hard to control, winter is great for flowering, Im sitting at 20-25 hum...did...ditty....I have always heard decreasing humidity is good for potency...I guess we will just have to see. (low hum. is not so good for nosebleeds though!!!!)