[gtojohn]

Short answer for your question, find a psychometric chart. The harder question would be applying it and making it work for you situation.
I was a broadcast engineer in my previous life. We had a 98kw vhf transmitter. Similarly we used 100% outdoor air. Honestly there was no good reason for that other than it had always been that way and the higher ups had little concern about inefficiency. Humidity and lack of it is your biggest concern. Too dry and static electricity becomes a threat. The more outside air you bring in the more energy required to reduce its temperature and humidity. You'll have greater control of humidity with less outdoor air. I would suggest a humidity operated damper to bring in more fresh humid air once humidity is below 20%. Probably more relevant would be dehumidification control with your variable speed blower. Lower fan speed more dehumidification. Most have a dehum terminal on the control board. Where I live its so humid its nearly impossible to dry air below 20%. Unless your building is unusually tight you're already bring in enough outside air to keep the humidity up. Good luck!