Direct Hit; how much is "enough"?

[Shurrikhan]

None have (in themselves; see the post directly above) diminishing returns, but two double up on their gains (Crit and Speed, as the first also enhances the value of the extra chance given and the latter gives the same flat GCD reduction despite that becoming a greater and greater proportion of the remaining GCD).

As such, unless dependent on Crit or Speed, stats like Det and (as it may be overtuned for most anyways) DHit tend to be strongest at the very beginning of an expansion, but are quickly surpassed by Crit or Speed if you can get either high enough (either one a vast majority of your secondary stat total).

Edit: In general, unless you need a specific GCD (DRG, SAM, etc.) or you get procs from crits (Bard), you tend to be better off either avoiding or stacking Crit/Speed. The secondary stat options of your tier will largely make that decision for you, however. By next, we may well all be pushing for Crit and/or Speed.