CHfather, will do. I currently have a regulator that goes up to 15 L/min and an O2ptimask kit. the system is working but does not keep up with my natural breathing. I am sure if I had a regulator that went up to 25 L/min I would be sitting pretty but my friends often call me overkill and I want to jump the the Porsche system.
My guess is the relevance of flow rate, with even a demand system, has to do with what flow rate you breath at. For example I now a demand valve with a max rate of 15 L/min would actually be worse than what I have because the reservoir bag would not fill up between the breathes. My understanding is the demand valve requires the effort of breathing to activate. My guess is the greater the vacuum created by your breathing effort the higher the corresponding flow rate from the demand valve.
After Spiny answered me I had a duh moment, there is virtually no difference in cost between the 40 L/min and 160 L/min models and the way I understand the operation of the demand valve, the extra capacity will not cause any problems.
I get my stuff the end of the week and I will post an update/review after I get it.
Thanks! Again, if it were not for this site and others like it I would be in a much worse state.