I definitely like the AC2, and having 4 of them in a build is surprisingly powerful. However, I think this build doesn't have nearly enough ammo (not even 2 tons ammo per weapon), so you're going to run dry really fast. I'd probably drop down to a smaller engine (or go standard engine) and fiddle with heat sinks and maybe drop endo-steel to stuff more ammo. I also love the MPL, but I think you'll get more mileage out of dropping to medium lasers instead, and using the extra tonnage on more ammo and/or saving crit slots by dropping endo or going to standard engine.
Even with everything elited you overheat after 20 seconds of sustained fire. Add in a bit of careful cover playing you might be able to stretch it to 40 seconds. 4xAC2 is so hot that you need more heatsinks besides more ammo as well. I don't see an easy way of doing that so when I get around to piloting, I'll probably stick to 2x2 AC5/AC2.
Burns through an Atlas CT in 6.76 seconds with just the ac. A large part of the Banshee's defense is the disruption from the volume of ballistics, so this can work. The other half is the armor and this is where I have a problem with your build. This: increases ammo, armor and speed. Standard engine:
Ditch the backup weapons, and go all in with the AC2s: Switch out a ton of ammo for a MLas in the head if you absolutely need a backup weapon.
I was fiddling around in Smurfy's Mechlab a bit, and decided to check out the quad-AC2 Banshee. I realize that these three builds are all very similar to what others have posted already, but none of them are quite the same. I guess you could say I've done a little min/maxing. The last two builds are also simple trade-offs from the first one, with the changes I mention. They all maximize on both slots and tonnage, and they all have maximum armor, except for only 67 in each leg. Fast, decent ammo, and MLasers for backup: STD engine version, which means it's obviously slower, and it also has one fewer DHS: Drop those lasers, and get REAL with an insane amount of ammo:
