CF290X overclocking help

[Born_2_Kill_83]

So I've been having a play with my Crossfire 290X MSI Gaming's, my maximum stable overclock seems to only be 1100/1400 @ 55mV, anything more on either core or memory I start getting a little screen flicker or perhaps the odd artifact.
I’ve seen other people pulling more than this with these cards, could it be I’m limited down due to running them in Crossfire?

Second thing is the temps, they appear to be fine at stock settings both in-game and benching but with the above overclock they hit 94c in 5 mins of benching and start throttling down, anything I can do to stop this? Again I suspect the problem might arise from Crossfire again, can any-one confirm. They seem to run hot for none reference cards.

 

[Born_2_Kill_83]

My case is a saw subject, I bought H440...cause it looked good , I now have 6 120mm fans pulling air into the case and one 140mm pulling air out but it still isnt enough when their enclosed by covers.

I'll have to try it without he side panel on and see what happens, I'd never be able to use anywhere near 100mV due to temps nevermind over it with the covers on.

 

[Born_2_Kill_83]

Can do but this then starves the CPU (Noctua) of air then