I was parsing for 10 minutes plus on each attempt. However, I must conclude that RNG such a critical hit, amount of fire procs at the end, thunder procs etc ... have a say in this. Although everytime I parsed using the second method I was around 320 DPS instead of 340. It was pretty consistent. I have thought about Yandere his or her remark as well. But I am really fast. You just press Fire III button very shortly and immediately move on to Blizzard III. I guess there is still a bit of time that is lost, but I would argue that in an 11 minute battle you perhaps accumalate how many Fire Procs at the end? Lets just say 20 hypocthetically. That's 20x250 more damage = 5000 over the second method.
How many more spells do you think you would be able to cast extra by using the second method? Enough to get that kind of damage over 11 minutes?
I must also continue to stress that you basically only lose just a fraction of time using my method when you do it right.