I actually did a full haste build in WotLK where I GCD capped my Holy Light (~1.00 seconds, was actually like 1.05), so that was the most extreme I've ever taken my haste to. The build was really solid, completely sustainable if you could manage your Divine Plea / SoW procs - and to be honest, it was probably the most fun I've ever had while healing. I'd like to try stacking critical strike this time around (when I get a bit better gear, I had quite a few more sockets at the end of Wrath than I do this early in Cata) - but I think we'll be looking at a mixture of haste and crit (40/60?), since our cast reduction spell is really powerful this expansion (
Infusion of Light - Spell - World of Warcraft - 1.5s on HS reduction of 2.5s spell) as opposed to last expansion (
Light's Grace - 0.5s [essentially passive] reduction of a 2.5s spell).
Coupling
Infusion of Light with
Daybreak, we're going to rely on critical strike to make sure we're getting that
Infusion of Light proc, and when it's not active, we're going to be relying on haste to make the most of Divine Light while HS is on cooldown.