Do they all preform the same or is there a difference?
Ok. First you need to understand that watts are a more accurate way to measure the power of your setup. Here are some numbers for you. If you are using a 3.7v battery and it has been used for a bit (because off the charger a 3.7v battery will read about 4.2v).
2.3Ω atty @3.7v = 5.95 watts
2.7Ω atty @3.7v = 5.07 watts
2.9Ω atty @3.7v = 4.72 watts
3.1Ω atty @3.7v = 4.41 watts
As you can see, the resistance of the atty greatly affects the power. Again, I have measured many 510's from Totally Wicked and NHaler and they are all 2.2 or 2.3Ω. I'm not sure why gratefulbuddy's are 2.7Ω
One of the reasons that mods that use large 3.7v batteries like the 18650 seem to deliver a better vape is that they hold onto that over 4v charge much longer than smaller batteries do.
A fresh of the charger battery at 4.2v with a 2.3Ω atty delivers 7.67 watts of power! What does this all mean? Choose your atty's carefully!