Do Rate of Fire Endorsements affect the Jet Gun in any way? I've tested it a bunch of times, but results have been too random to help.
I would too, but a test between no endorsement and Gold endorsement used up the same amount of ammo in a period of time. I've tested it for damage output, but with no real way to test it, I've had to just time myself when killing bouncers, and they were about the same between no endorsement and Gold.
It increases how fast you burn through your Jet fuel, which means that whatever you're targeting is (essentially) getting burned more by an increase in Rate of Fire. The reason your testing was too variable is because there are crits to be accounted for, burn damage stacks on top of the damage being done by the Jet Gun, and the fact that being closer to its nozzle does more damage.
Well the thing about the jet gun is it deals more damage the closer you are, so it's hard to test accurately. Where RoF really shines is with the rail gun, but it does also affect the RoF (DPS) of the jet gun too. When I first started playing tank way back when, I used gold RoF and I remember the increased damage being pretty obvious, but it has been a long time. The build I've been using forever now uses bronze RoF. Uber has said certain guns when run with gold RoF don't actually run at max potential because of frame rate issues, that could be another reason you don't see such a difference.
In my case, play as a speed tank and try and fight a RoF tank in jet gun range or vice-versa. The battles are pretty one sided to the favor of the RoF tank. Speed tank is still a blast though.
RoF affecting the Jet Gun isn't as important as it affecting the Rail Gun. Changes it from clunky, finicky crap into a rapid fire, long distance bot shredder.
I notice Crit effects the jet gun just as much. Notice the changes in shape of the flame? That's when the crits are kicking in. Crit Rate Armor Lethal!
Gold Crit Tank is simply a Base Destroyer. To test if it works is easy. Take a non-Crit Tank and shoot at a wall, now do the same with gold Crit. You'll notice the color of the flame touching the wall is purple which indicates it's critical. While gold crit. is decent for armored Pros it is a monster against Bots and Turrets. The reason it's average against Pro is because they are mobile. The closer the enemy Pro is to your nozzle the better change to kill/hurt them more/faster.