It's my opinion that if 130gr bullets are an optimum weight in a 270 Win, then it's even a better choice in the 6.5 calibers.
It's also my opinion that the Win 780 load range for the 6.5x55, listed for the 140gr bullets, would be safe to use for the lighter 129-130gr.
Being that Win 780 is a ball (spherical) powder, I would use a magnum primer to develop my loads, because that's my criteria when using ball powders. They are usually harder to ignite, and 780 is a pretty slow burning powder, and if you work up the loads, it will only give you more consistent ignition.
You can do as you see fit though.
NCSmitty