Get a spare spool and load one of each.
I've used a 7500SS on a similar St. Croix rod for the past year for plugging, tins, eeling and the occasional chunk or clam. One spool has 20# Big Game and another has 50# Power Pro. I prefer the braid.
It seems people either love or hate Power Pro. There is some stuff worth reading on this post.
http://www.striped-bass.com/vbulleti...&threadid=8228
It took a couple days to soften up the line and I learned the hard way not to overfill the spool.
I don't know if the 6500 shares the same bail trip issue with the 7500 but I powercasted a couple plugs to the horizon until I converted the bail to a manual pickup.
I haven't had any problems since but I am now also more attentive to how the line is laying down on the spool.
You should still be under your initial budget so go spend the rest of that money.