My bike quits almost immediately when it hits empty, and usually I can't get it switched to reserve in time to prevent having to pull over, or at least coast and restart, but the bike usually starts immediately after I switch to reserve, too. The stock petcock, and those on every other bike I've owned, with or without vacuum, would sputter a couple of times but allow me to switch to reserve and keep the bike running.  Not the Raptor.

Nothing inherent about a Raptor, or any petcock that will make too much difference...
... after all it's only a tube in a tank...
It can make more difference if you're going uphill or downhill, or turning right or left....
As far as flow goes... it's got to be faster than a vacuum petcock if anything... no vacuum mechanism to obstruct... it's a straight shot....

I think circumstance will make more difference than type of petcock...

I've caught it on the sputters most times it is signalling "reserve" when I was rolling at some goodly speed and had a few seconds of momentum to utilize.   Still, it comes back FAST in 2-3 seconds once you flip it to prime and you can keep on going.

If you are in stop and go traffic and have no momentum going, I can see it stopping you since you don't have the 2-3 seconds before stopping anyway.

Down is normal, aimed horizontal to the front is off, up is reserve.

Memory jogger -- when you need reserve, point the lever up at the tank ....

I have only run ot a cople of times with my raptor.  Once, I did not need to switch to reserve, I was pulling into the gas station and just coasted to the pumps.  

I also have a big plastic fuel filter in line, something for a car that came from Wal-Mart for a couple of dollars.  It stands to reason that would take some time to fill, but not long.  I don't recall any delay in being able to get going again.  Somewhere there was a discussion about the filter not having to be full or not looking full or something and that is what I found.  If that was a hijack, sorry about it.

I don't remember any delay or difference in that time and the few other times I had to go to reserve with the stock petcock.  But I try to get gas every 100 miles and really don't use reserve much.  (Yes, sometimes I switch, just to keep the thing broke loose, but notice no difference in the way the bike runs.)

here is my exp for what it is worth - had to hit reserve on the stock PC once learned my lesson shut off right at 2 gal used had roughly .2 gal  left in the tank........this week i knew i was going to get close to my 100 mile fill point while out on a ride so i put the raptor on reserve before i left the house so I would not have to flip the switch in mid-ride-mode......well i made it to the 101st mile without a hiccup pulled in and filled the tank...it held 2.238 gal......not sure how that was possible without it having a hiccup or flat out cutting off......

Likewise, my bike will stumble once or twice, I reach down turn the raptor petcock to RES and keep on going, I too have a fuel filter but don't know if that has anything to do with the float bowl level.

Everyone should turn their petcock to reserve once in a while, to keep things limbered up.

But don't forget to turn it back to on.  

Don't ask.