5k and likely 6k series cards detect fine up to 8 cards with, I'm assuming, all driver revisions. It's the 7k series that has problems. Reportedly you -can- do 8 7k series GPUs but only with the 7990's. You can run up to 4 GPU on win7 with driver 12.8 or higher, 5 GPU on win7 with driver 12.6 or lower OR win8 with 12.8 or higher, and 6 GPU on win8 with driver 12.6 or lower (requires special installation steps)
Thanks for the final details dude
In my current setups in relation to heat and other factors 5 x 7xxx seem to be an ok template for me at the moment
I am commissioning another site and will look at 6 card rigs...
Dont the 7950's and 7970's have troubles using the old drivers when trying to use conncurrecy above 8192
i.e 7950 21712 ltc mining concurency setups