1) Looks right
2) Yes, I meant physically remove a card
3) Not what you want
4) That's specs, I need a model number. Look here for a list of all their Z87 boards:
http://promos.asus.com/us/z87/comparison/ . My mistake, it's a Z87-A.
The spec page here,
http://www.asus.com/Motherboards/Z87A/specifications/ , says
Expansion Slots
2 x PCIe 3.0/2.0 x16 (x16 or dual x8)
1 x PCIe 2.0 x16 (x2 mode) THIS IS THE SUCKER
2 x PCIe 2.0 x1
2 x PCI
So the third slot is physically x16 but actually PCIe 2.0 x2. Max theoretical rate 1 GB/sec in each direction.
Go back to question 2. Remove one graphics card and put the Revo in the other graphics card slot. If it's running near expected speed, you have identified the issue and we look for a mobo with a third slot that will run at x4. Hey, I forgot, is the Revo PCIe 2.0 or PCIe 3.0?
EDIT: "The RevoDrive X2 family gets its edge by employing a PCIe x4 interface (1GB/s bandwidth as opposed to 3Gb/s of SATA II) " At 250 MB/s per channel, that's PCIe 1.0. You need an x4 or higher slot. PCIe 1.0? Really? How old is the drive?