UAC i don't know. Not sure if I still have any numbers handy i'd have to dig around. I want to say 20ish for a small weapon -> large weapon situation? I never did any testing to see if, say the DF or crit weighting, etc. changed. I don't think that it does but that'd be a nice change!
The biggest benefits isn't the AS/DS improvements for melee weapons, but those are quite nice. The biggest benefit is how it absolutely destroys the targets bolt AS, which if you're not using a shield is HUGE. I want to say when I first got it i was hunting nonominos or something and it took their bolt AS from something like 200-300 or whatever they have to about 80? It was a huge improvement. It also prevents certain movements. I.e. if you knock something down, and press it, it can't stand back up. So what I actually used it most for was on multiple creatures knock down one and press it, it couldn't stand, then kill the second.
It's pretty expensive unfortunately, so it's hard to use regularly.
My experience was with small weapon TWC (sais and katars), for reference.
Mithrilschlong, 2015-03-10 to slightly later on 2015-03-10. You will not be forgotten!
usable Meteor Swarm, late 2020-12-30 to early 2020-12-31. You will also not be forgotten!