Well, from what I've heard chance to hit is something like... Math.max(a, (b-DV)/DV)... in which a is some constant (like 5%?) and b is monster bonus to hit... If monster has lower to hit than DV only a matters.... but with fairly high DV division makes right part less than earlier.
But that is just theory anyway. I think practical evaluation was that DV effect caps at ~70.
Bugs with multiple rolls and PV ignoring are really antismithing stuff.
So far rolled 15 casters with RoDS and shamelessly killed them within 200 turns. For eternium glory!
(after 15 I stopped counting...)