dacron and gellspun

[tailingloop]

With 20lb Dacron you get a 50% to 60% increase if using 50lb spectra braid (gsp is same thing). With 30lb Dacron you get a 80% to 100% increase if using 50lb spectra.

As you surmised, much depends on the diameters of the lines being compared and how you lay it down on the spool.

I wouldn't use spectra braids of less than 45 to 50 lb strength for backing as they are much more prone digging in to itself when winding it back on the spool after a fish has taken some backing out. You are also more likely to cut yourself with the thinner backing. Knot strength is always a factor with spectra lines so 50 lb will be a bit more forgiving in that respect.