Crit Details - Keen & Boosting crits

[NorthHelix]

Hi All,

Could someone please give me some more details on how crits work.
Other than "Keen" how else can i extend the crit range of a weapon? Are there any enhancements, feats, skills, or spells that do this? I realize that Keen and these others would not stack as per the description of keen, but that would allow me to use the keen bonus for some other type of bonus.

Also I would like clarification on how Keen works. Let us Scimitars for this example.

Scimitar (Copied from the compendium section)
Damage: (1-6) 1d6 + 0 Slash
Critical Roll: (15%/2-12) 18 - 20 / x2
Attack Mod: Strength (+2)
Damage Mod: Strength (+2)

Keen: This ability doubles the threat range of a weapon. This benefit doesn't stack with any other effect that expands the threat range of a weapon.

A normal Scimitar has a 3 point crit, so am i correct that a "Keen Scimitar" would have a 6 point crit, making it 15-20?

I am currently working on a Dual Scimitar wielding ranger/FvS. I wan to get the crits up, without killing the other stats too much. I just hit level 4 an i'm really enjoying the character. I just picked up 2 Rusted Shamshirs.

Does it make sense to dual wield two crit weapons, or should one be just a straight +X and the other for crits.

Thanks to all in advance.

For Reference, copied from the Compendium:
Rusted Shamshir (Scimitar)
Damage: (3-8) 1d6 + 2 Slash, Magic, ColdIron
Critical Roll: (15%/6-16) 18 - 20 / x2
+2 Enhancement, Keen, Cold Iron