Usually you should keep crit rate and crit chance as balanced as possible (so for 40% crit rate 140% crit damage; for 50% crit rate 150% crit damage). In practice, crit rate suffers from scaling, to almost 50% against same level enemies and reduces further against higher level enemies like ABX Frost Beast and World Boss. Thus you should technically go 2:1 for crit rate/damage. For uru the setup is actually 8:3 for optimal ratios since you get more crit damage per uru than crit rate (an uru of same rank gives 33% more crit damage than crit rate IIRC).
Again, GC and crit rate buffs from active skills WILL skew the results so take that into account too.