Once you hit 79% on your character sheet Crit falls way, way behind Haste in terms of RPS. At that point you decide whether you want more DPS (Crit), more Armor (Mastery) or more RPS/Mitigation (Haste).
Personally I'll probably be going for more Haste at that point.
As for the 2pc/4pc bonuses.....
The 2pc bonus is kinda boring. Depending on how it works you could theoretically get a full minute of constant SD (or maybe a bit more). The SD portion of it will always be useful, while the FR portion will be kind of random.
I actually really like the 4pc bonus. We already have an incredibly strong on-demand heal in FR, we don't need another one. This bonus is very deceptive in that it appears weak, but the amount of healing you're going to get from it will be ridiculous.