1) There is no TRIM support for SSDs in RAID configuration yet.
2) Garbage collection is internal to the drive and does not depend on motherboard or drivers. Dang - I had a link yesterday to a good test that someone did, and now I can't find it. I'll edit if I see it.
Different SSDs run from decent GC to ineffective GC to no GC, so do your research carefully.
Can someone else here point out a utility that will TRIM or otherwise condition SSDs in a RAID setup?