Gam3r01 :
6 pins deliver 75w where 8 pins delivers 150w.
You can try it, but if the system is unstable you know why. I dont recommend it.
I've just upgraded from a HD4890 which used 2x6pin power leads to an XFX 7870 which has 1x6pin & 1x8pin and it
WILL NOT display anything with a pin plugged in to the 8pin socket, despite an article I read on here which said that it might because the two missing pins are only ground pins. I realise you have a different card. Just wanted to help out where I can.