So basically this is from a dummy fight I did with a hammer, with no stone at all. I think a few mathematical things are a bit off but this is basically correct.
Using 31/24/11 Druid Shaman Inq
4:45 fight on the boss dummy.
211804 total damage done.
Magic Crit % Avg=31.67%
Physical Crit % Avg=39.40%
Which would give
Total Damage % from Magic crits 21%
Total Damage % from Physical crits 13.79%
44478*1.15=51151 Magic Dmg with a witchstone
29207*1.15=33589 Physical Damage with a weaponstone
6673/285 seconds =23.414 DPS increase for a Staff
4382/285 seconds =15.375 DPS increase
So in conclusion according to witchstones/weaponstones, a witchstone will be ~8.039 DPS increase over a weaponstone.
NOW I had this in my guild forums, and now I started thinking a little bit. A witchstone actually only increases crit from a SPELL. A lot of those elemental attacks aren't actually spells. Some of them won't proc a trinket "on damaging spell" so I don't think it gets the benefit of the witchstone. I don't really feel like doing math again, but it is basically a wash or very minimal using one over the other.
Now on the otherhand, and I have not tested it, as I do not have a 29 dps dagger to use. But a 1h dagger and a whetstone on paper is actually better than a 2h
It adds 12 damage,
12/12 Min/Max at 1.8 is a 13.3 DPS increase on the weapon.
If it is just 12 min or Max, it is still 6.667 dps on the weapon.