Gun Stats
I disagree. I have found that all the stats reflect what the gun already has. Go to one of the mines like the lost cave and shoot a crystal stub to see what damage your gun does. Try one with zero proficiency, you find that the gun does exactly the damage stated in the damage stat, the -30% or +30% will make no difference.
It seems that the +/- indicator is just telling you what the gun does over a baseline for a gun of that type.
Well, a cristal does not have critical damages, so that's a factor for damages only, but on Craw my 1000 something damages bessie does it at 5000/6000 damages...
It's still a little confusing weather it works or not and that we actually need a gearbox employee or somebody who actually knows about this stuff to tell us what it exactly does!

Yes it does, as an exemple find a Sniper that has whatever critical hit bonuses and shoot a guy in the head you'll have your answer ;)
Time Spent on Borderlands : 1700 Hours +