I dont know if this has been mentioned in this thread so here goes.
The trick wheather you use a nose clip or not is to breath out while your face is in the water and so all you have to do when the nose/mouth is above water is inhale. Using this method there is lots of time to inhale.
Hi: Sorry, what I mean is breath out thru your mouth while your face is in the water. Does that clarify it for you?
May we swim with ease at the speeds we choose.