There are 3 split rails on the bp550plus, I cannot find which rail is for the graphics card. Also, how much Amps does the sapphire 6850 need? Is this power supply ideal for this build? Do I need a higher watt psu for this build?
The cord for the GPU is the only plug that fits your card. Its one of the cords that unplugs, Its marked with a RED modular plug on the side of the PSU. Its pinned so it fits only that plug. It has a 6 pin end so you will be able to power it with that PSU. (there is also a 6+2 cord hard wired into the non-modular bundle)
I just did a new build yesterday with that PSU and a Sapphire 6870 card.