I personally don’t think that it has anything to do with the drives. I’ve used my G-Raid for 1:1 and DV50 for about one and a half years now with no problems whatsoever. My G-Raid is also connected through firewire 800.
I could sell you a Quadro Fx 3000. I have one for sell that I took out of my system because I just changed motherboard and processor to the new core 2 duo and had to buy a PCI express FX560.
Yes it works with Media Composer and Xpress Pro. I am building one as we speak with the E6600 and the Asus P5W DH Deluxe. Check the Avid forum, you will see that it is working good.