I think it's a toss up.  Less of either does mean more product flowing through each tube but it also means more availible air to move it.  I've never seen a tube plugged because it couldn't flow enough product.  I've seen lots of them plugged because they didn't have enough air to keep the product moving. 

Our 1600 Flexicoil handled both meters at full rate moving at nearly 10 mph with 27 runs covering 42 feet when I proof tested it after setting up.  I estimated the rate (meters were off their scales) at approximatley 400 lbs of 68 lb material  Our normal application was in the area of 196-238 lbs and operating at 8 mph.  Plugging was not a problem unless there was something wrong somewhere....chunks in the fertilizer, moisture not dried out of the hoses before starting, plugged boot,  dumbass left the tank lid open, etc.  The only way I know how to set the fan speed is WFO.  If there is a disadvantage to "too much" air when carrying fertilizer I can't figure out what it is.   Tube wear maybe, but as long as they will last a season I don't really care about wear. 

There are, or at least used to be, lots and lots of 200 bu plus tanks in Canada.  Used to be cheap because of the exchange but I understand that may be different now?