Re: GTX 280 and Power Connection
the 8 pin connector only provides up to 150W of power, which would be 12.5A @ 12V. As long as you're using any two connectors that can make up that much power I think you'll be okay. I would assume that P15 and P3 is on one rail, and P16 and P4 are on another, which would put those rails at 16A each.
You might want to use one of the connectors marked for 10A in the 6pin slot as technically a 6pin connection is 75W where using one of the 6A would only provide 72W. I doubt those connections only provide 6A but you never know.
I would go with what you were thinking and use P4 and P15 for the 8-pin, and P16 for the 6-pin.