the slot doesn't make any difference, you'll get the same hash rate on an x1 slot so its not that

I agree you should remove the crossfire cable (you'll need a dummy plug though) ... but even with it on those speeds are off - you should be ~350+ with that card pretty easily

You sure the first miner is set to [0-0] Cayman and the second is [0-1] Cayman in the drop-down?

What power supply do you have?