I dunno, as awesome as the rest of it is, nano-BFG will still take a crapload of time to restock its ammo. It seems to me that the regeneration of equipment comes at one per "action unit of time", which is some separately-defined amount of time dependent on each action, which is in turn dependent on mods and boosts and such. As a result, the only time I have NOT seen equipment recharge at one/action is during berserk, where actions appear to be roughly halved (meaning it would only recharge at a rate of one per two actions). For a weapon that takes 40 cells per shot, recharging is a rather large hindrance: the only saving grace is that nano-charging weapons are not limited by self-sustaining ammo only and can be refilled when necessary (contrast: nuclear weapons, blaster). Nano-Railgun would face the same problem but on a greatly-reduced scale.
Honestly, if you could GET that? Assuming the enemies will even survive five shots, all you need is some cover and you're golden. As a wide-scale annihilator, there is no better killing machine. (Seriously, 13d8/~0.60sec, with like a 10-tile blast radius, you wouldn't need five shots to clear freaking N! Mortuary.)
Given a simpler option, I'd love to get my hands on a P3N1 combat/assault shotty. 10d3 at a distance and infinite shells ensure a complete victory if you're careful enough.
In practice, however, I haven't seen better than a MAc-fueled BFG10K from my N! A100 run. That thing rips up the game. If I did manage Cyber-nano and DS, I think that would trump it. (Unfortunately, BFG10K has a wicked kick that occasionally hurts you.)
I'm bored with this character now, so I'll probably retire without even finishing. It's frustrating to be running around after viles and revenants while mancubi blast them all away from you, and I always found melee boring in doomrl (If I wanted melee, I'd be playing adom). :)
Just because you have an ultimate combo doesn't mean you have to go for YAAM (or at least YAAM since you picked it up). Rushing for stairs can make the game go by pretty quickly, even on A100.