Hi,
 
Whats the difference when using 2x 8(6+2)pin vga powercables vs 1x 8+6pin vga powercable with one gfx card? which is preferred? one or two cables?
gfx card is original gtx titan.
 

Yep..Depending on the power supply, the one 8-pin + 6-pin cable should work fine, but in some cases it has not and using two seperate cables works..If one cable works okay, just use the one, which is what I would do..You can use two seperate cables if using just one don't work or if the extra cable clutter isn't an issue..You can try it both ways if you want to, but I doubt it'll matter at all..With your single 70A +12V rail SuperNOVA 850W P2, just one cable should more handle it okay like EVGATech_ErinW said.