I'd recommend the headstart, unless you would much rather have and khaki line than a neon yellow one.

I love the XXD, but wouldn't recommend it for this situation. While the belly of that line is front loaded, its front taper is much longer than that of the headstart, and still longer than that of the GPX. The taper will have more to do with kicking over weighted buggers and poppers.

The XXD is my favorite line ever for long casts, long mends, and long roll/spey casting. I doubt that's what you'll be using the 8' 4wt for.