First, I'm no genius so don't expect me to straighten you out
I start recirculating my mash as soon as I have my hands free from mashing in. I start VERY slowly for the first 10 minutest or so. I then gradually increase the flow. Since it's just recirculating, I can't really tell you how many GPM's or the exact flow rate. By the end of the mash, the flow is pretty fast, not full open, but pretty close. I have an in-line site glass and at higher flow rate is when the wort becomes very clear.
BTW... I have a RIMs system.