I have never used Spectra myself but a good customer of ours makes annual jaunts to Christmas Island in search of Giant Trevally.
He loads up pretty much all his reels with, I believe, #50 (about #15 mono) Spectra. He loves the suff.
Word of warning though, not all Spectra is created equal. The only Spectra I will fish is Power Pro. Its the thinnest diameter Spectra there is but is still soft. It is much stronger and has a higher abrasion resistence then most other Spectras on the market like Fireline, TUFF Line and Spiderwire (pure crap!!)
Ryan S. Petzold
aka Sparkey and/or Special