Why not pick up two 5970's , instead of four 5870's?? It will give you about equal performance (quad crossfire/sli have never scaled great), plus give you room to grow. At that point you can drop down to a good standard X58 MOBO like the ASUS P6T V2 Deluxe.
Why do you need four SSD in RAID0 (guessing at the setup)? You won't see much difference running two in RAID0 over having four. Your eye can only see data so fast, which you are getting to the point where you won't be able to notice a difference.