3 out of 4 GPUs mining slowly

[transposon]

I have a MSI Z77A-G45 with a ivybridge celeron.

There are 4 7950s connected.  When I start hashing all of the cards go up to around 640 kh/s.  Then all of the the cards except for the primary (the first x16 slot) start falling and settle to around 580kh/s.


Any Ideas whats going on?   Could it have something to do with PCI latency or some power saving mode?