Shield recharge delay and reload speed are calculated like this: Let’s assume you have a gun with a reload speed of 5 or a shield with a recharge delay of 5 and a skill with +20% reload speed/recharge delay. 5 / 1.2 = 4.167 seconds reload speed or recharge delay. The +20% adds to the divisor of the base stat. So you can stack them as much as you want, but reaching 100% of either stat just leaves you with the base stat divided by 2.
Fire rate is probably theoretically infinitely stackable, but FPS limits it at some point. Elemental Effect Damage, Recoil Reduction and Recharge Rate should all stack forever.
(Flying: throwing yourself at the ground and missing)
Gearbox math is done in such a way that you shouldn’t get any of the reductions to the point that you have zero delay, immediate recharge, etc. It’s mostly because the bonuses are not all handled additively. You can get the general idea from looking at the various formulas that have been derived from studies of in-game stats (examples below). As mentioned by one of the other responders, maximum fire rate is effectively capped at frame rate.
The thing with the BAR stat boosts is that the increases get progressively smaller as you rank up. At around 150K BAR, a 19% boost will go to something like 19.3% with one extra point; that drops to 0.1% increments at some point, and it becomes prohibitively time-consuming to get each successive increment.
I’ve played and farmed my BAR up to 839,000 so far My highest stat so far is Gun Damage at 91% the rest of the other 12 Perks I’ve picked are between 35% to 55%. I know when I apply a new BAR Point to Gun Damage its 1 = .1, though once in a while it gives me .2 for 1.
I do know that Gun Damage can stack past 100%, as a friend of mine whos played a little longer has got it to 102%. I am assuming at this time that all the perks are able to keep going past 100%, though at this point I have no Data, except for the one friend, to support my assumption.
I can say that my friend and I have been able to pump up the Gun Damage perk by just picking a set number of perks (13 for me in BL 2 and 10 in TPS) which has allowed us to focus our BAR points to just the perks we want,
I have updated my forum thread to show my old BAR stats with my new BAR stats here, though I have got side tracked and haven’t focused on putting my thoughts and theory’s down as I should
I do use a level 70 Doppleganger in TPS to power level using the capture a guardian mission, I have Gun Damage in that game at about 55% at this time, combined with money is power, I can average a kill (with a level 66 gun) every 2.5 seconds if money is power is maxed out (999 stacks) I get 1 kill per just a little under 1 second, any faster would freeze the game and if I raise Gun Damage higher I may have to lower the level of gun used.
In BL 2 I do look for any mods or skills that also helps increase those skills you have mentioned (same ones I have), I just have not experimented much to see how they stack up combined to each other, other then it’s a lot easier to kill such and such raid by using this , this and possibly this.