SSD and HDD switch works for me. I was looking a the Crucial M4 128Gb, but it wasn't in stock and a little more$
I was going to go with a single PCIe 3.0 MB, but you said maybe on SLI, so I wanted to leave the option open to you. the AsRock MB works for me also.
the 7870 vs the 6950 the 7870 is a faster GPU and is more efficient. it ultimately your call. the 6950 isn't a bad card for gaming. it does run a little hot, so it you are putting the rig in a warm environment then you should go with the 7870.