Haste and You... A guide to the misinformed.

[Frost]

yeah, now if you can combine fast cast gear and haste gear, that would be sexy ^.^

Actually....
You can....

Fast cast initializes at the start of a spell and carries through to the end; Haste only needs to be on when your spell is completing. So if you start a spell in fast cast gear and end in Haste gear you get the best of both worlds.

Personally I start casting in say on thief: Anwig Salade(3), Magoraga Beads(10% cast time), Mirke Wardecors(5), Loquac. Earring(2), and Homam Cosciales(3), and end in 29% haste(overkill, but it's just how the gear works out). So I take 23% off the actual casting time, and 25% off the recast (Technically something like 36% off the recast inclusive).

Taking that a step further, you can pile in Fastcast gear, Spell interuption gear, and evasion gear at start, then switch to evasion(changing pieces you no longer need) and Haste towards the end of a spell, you get the FULL benefits of your gear. You only gain in that, since you're not attacking while casting, there's no harm in going fully defensive.