If you're concerned about capping crit rate from Atma like Naraya was hinting at, I'd check recent pages of BG's major Atma thread. Melphina and Vegetto both had samples indicating a 50% cap from Atma, but sample size could be an issue so I'd still keep my eyes and ears peeled on the most current info as it comes out. Either way there is no global crit cap at 75%. If crit even globally caps it should be at 95%, so I think your crit+ dagger is safe, OP.
As for which is better, I'd have a hunch the base dmg is better, but playing with some napkin math might prove me wrong. It's hypothetical but, say you were at 1.0 pDif. Crits would hit at 2.0, doubling damage. Let's say you had two base 35 daggers. Your crit rate effects both of those daggers. So with crit rate +4%, that's essentially a 4% chance to double either of your daggers' base damage. Equivalent to an 8% chance of doubling a single daggers base damage. So consider (35)*0.08 vs (5). The number to the right of the 'vs' representing the bonus from the base damage+ dagger. To the left, the bonus from the crit dagger.
It comes out to a number less than 3.5, vs 5. So it looks like the base damage dagger would win according to melee DPS. Unfortunately if you wanted to be really accurate, you'd have to consider WS dmg as well. Evisceration with dual wield is a 6 hit WS. Only one of those hits consider the base damage of your offhand dagger, whereas the rest are your mainhand. So for WS if the base damage+ weapon is in your offhand, it's doing a lot less. You only get +5 base damage to the total base damage of your WS. Whereas that "less than 3.5" I mentioned, would be added for each of the 5 other hits. In addition, it'd be bigger than 3.5 base damage, since the crits aren't coming from a 35 base-dmg dagger, but from 35base damage + damage from evisc's 30% dex mod.
So the crit one definitely wins on WS if it is in your offhand. Question is, which dagger helps more for your overall damage. I won't figure it out for you, but just offer you the above as food for thought.
Edited, Dec 30th 2010 7:11pm by Shamaya