Well, great, now you got me curious. Okay, let's do some calculations(in the spoiler block). We'll assume nonmagical weapons(as identical enchantments contribute identically), and that our rogue hits on an 11 or better.
Only 20 is a critical:
Rapier: 0.45*4.5 + 0.05*8 = 2.425
Katar, Heroic...