What is said above is true - but only within reason so you need to take it with a grain of salt and apply some common sense.
With two tanks of more or less equal size and roughly similar pressures (1000 psi difference or so) it makes no difference as the amount of change will be minor.
However if transfilling from a large tank to a small one, and especially if going from zero to 3000 plus psi, as would be the case if refilling a 6 cu ft inflation bottle off a 3500 psi 130, the small bottle is going to fill very fast if you just crank the valves open and it will get unacceptably hot.
I used to see a lot of SCBA tanks that were slam filled by fire departments in 30-45 seconds. The number of cracks and hydro failures was impressive in tanks abused this way. I would not do it to one of my tanks.
So I'd suggest using some common sense and keep the fill rates slow enough so the tank being filled stays cool enough that you can keep your hand on it without it being uncomfortable that will limit tank shoulder/wall temp to around 105-110 degrees F.
In the end it makes no difference in how long it takes to transfill the tank. if you do it fast and heat up the tank, you have to leave them connected until the receiving tank cools to get max volume in the recieving tank. That will take you just as long as filling the tank slowly in the first place, but the latter method prevents any long term issues with heating and slam filling the tank.
