Ok, let me tell you something: the FABER cylinders are designed for 10,000 cycles to 4,000 psi... (yes, these are the LP ones, filled to 2640)
I think they are plenty safe enough to fill to 3500 psi.
As far as the DOT is concerned, they pull alot of stuff right out the air. Please dont defend the DOT. They are just another government agency that sometimes does things without having a CLUE...
[edit to include:]
ALso, the 3AA designation is over 60 years old!!! Thats right, it was around before world war II. Do you know where the 10% overfill came from??? HMmm??? It had nothing to do with any tests, or designs or metallurgy experts... It had to do with a shortage of pressure cylinders, so they had to get more out of each one. thats where the overfill came from. So, basically thanks to that, we get to overfill these tanks. Now, do you think the metal has stayed the same since the 1940s??? NO, actually the steel alloys that they use now are stronger, and can handle more pressure...
HURRAH for Pressed Steel for finally changing from 3AA to a designation that actually Makes SENSE!!! E SERIES...