Anyone know if OB is rolled vs the sum of DB+PB or vs each separately? It makes a difference in whether one should try to maximize both DB and PB or if if it is better to try and raise one much higher at the expense of the other.

Points can flow between OB and PB (with wimpy). DB relies only on eq worn and how much you carry.

PB is split when you're fightding several people/mobs. DB isn't.

3OB gives 1PB on wimpy.

That is actually a very good question. And I don't know the answer to it. I'd like to know though... it would be quite useful!

It would make quite a diff, e.g.:
attack 100 vs 50db+50pb=100def is 100/100 50% chance to hit
vs.
attack 100 vs 50 db is 100/50 66.6_% to hit AND
attack 100 vs 50 pb is 100/50 66.6_% and you need to hit both times to score is .6_ * .6_ =.4_ or 44.4_% to hit.
Which means if you split your efforts equally on parry and dodge you get hit about 5% less than if you go whole hog on just one.

It would make quite a diff, e.g.:
attack 100 vs 50db+50pb=100def is 100/100 50% chance to hit
vs.
attack 100 vs 50 db is 100/50 66.6_% to hit AND
attack 100 vs 50 pb is 100/50 66.6_% and you need to hit both times to score is .6_ * .6_ =.4_ or 44.4_% to hit.
Which means if you split your efforts equally on parry and dodge you get hit about 5% less than if you go whole hog on just one.

Well anytime that you are fighting more than one opponent PB is split so it makes more sense to go for max DB.

Also since bash depends on DB, why do people insist that you assist to help bash.

Bash is not only counted against DB, if you had ever tried to bash something hard to bash with and without parrysplit you would have known that.

While DB is more valuable than PB it isn't quite as simple as that in practice since to get that DB you have to sacrifice more than just PB (and mostly not really any PB at all).