Just wanted to know at what stage a single pump becomes obsolete?

My Last trip to see Mark@MAD he said I was running a little lean at the top end and may have pump issues!
Well I'm planning to take it back soon for a little up in power and wanted to have it ready for him.
Hopefully I'll get a chance to check flow this week on the single pump and have been advised I will need around 4.5 liters per min??

Bosch quote the 044 pump as 300 LPH so 5LPM and 72.5 psi am I chancing it running close to the max output of the pump or does the fact that I will hardly ever be flat out mean that a single is sufficient?

Mark also said that the leaning out at top end could be to do with the Aeroquip a1000 regulator I'm using! So I guess they are either shit or it may need adjustment.

Any imput Appreciated