well, It turned out it's the power. I had connected the card with just one pice cable (6pin). So when it went under load, system BSOD.
So I got another pcie (6+2) and plugged that in, with 2 cables the card was stable, but the clock was all over the place.
After running on load the second card would not clock down, tried enabling and disabling crossfire, different drivers but nothing.
Card running idle at 77º and 115º under load.
So i unplugged the 6 pin, leaving the 6+2 in, card went back to normal temps.
When i look in realtemp it shows me the asus card (number 1) is running at around 1.095 v, while the powercolor (number 2) is running at 1.315 v.
Didnt have enough time to keep testing.
edit: cleaned out thermal paste, applied new one, temps are back to normal. noob mistake, it's my first time pulling something like this. On the other hand quite happy with results, went from ~45 fps to ~95 fps in BF3.