Hello,
I've found fastload combat shotgun really early - level 3, before Hell's Arena - and decided to try and use it. Normal reload on combat shotguns already works slightly faster, so I though "why not?" To my surprise, I managed to fire/recharge 4 times point-blank at a Cacodemon without retaliation! (The caco in question is long dead, of course:). I'll try it some more but I managed to pull that trick again with the same success, so I suspect reload time on it is really waaay down.
Once I get to Knights/Barons it will be a different story (here hoping to get to double SG before that).
FWIW,
Zarin.