4# Fireline. Just look at your reel's spool capacity.
Go with 6# mono, should be light enough for pannies and have enough for big bass. I have 6 on my ultralight, works just fine for me.
How come you have braid higher then fireline? They are relatively the same diameter and strength. I personally would stay away from fireline fused lines, fireline braid is OK but power pro braid is the best IMO. I recently switched to silver thread line, I love their fluoro and would highly suggest giving that a try.
Sorry Bob there is no basic thumbs up without the crazy smile. But your reccomendation is perfect.If you want to go heavier on a UL then you don't belong using an UL. Thats what drag is for. I would ask what you cast with #6? I have a lot of stuff thats a pain to cast with #4 let alone 6.