My ultralight set up uses 6 lb Berkley Fireline -- which has a diameter similar to 2 lb test. PowerPro also makes a 6lb test 2 lb diameter.
It's very fine, almost like fly tying thread. It may be too fine for your tastes -- but I like it because it is very sensitive -- very hard to see (good for fish, bad for my 45 year old eyes) and if I get hung up, it's strong enough to straighten a hook and pull free.
That said, I'd recommend it for a spinning real, but I think the Synergy is a spon/cast reel, correct? If so, look at P Line FluoroClear -- a fluorocarbon mono mix. Best of both worlds, IMHO. it comes 2,3,4,5 6 and up in lb test -- maybe try a 4 or 3 and see what you think.
I build many of my own rods and this little ultra light started out has a handle mock up for a St Croix catalog. I finished it out, and it now lives on the farm with the ponds. There are days I miss it in the boat -- but it's at home on the farm.
