Long story short - I run FusionIO cards in production (4 X 1.2TB DUO Cards for one logical drive and 2 X 640 DUO cards for 2 logical drives).
Well, come to find out the FusionIO cards need to placed specifically on the PCIE bus in a specific order. Our production servers (with the physical different drive layout) work without issues.
I builtout a new physical server (HP980) with FusionIO cards and performance was horrible.
So - after multiple server rebuilds - we mimicked the exact FusionIO physical card location from our primary principal node. Now the server behaves as expected.
Now, all the 1.2 TB Duo cards are sitting on Gen8 slots and the smaller 640 cards reside on the Gen4 slots.
So - if running FusionIO cards, make sure the cards in the correct Gen slot.