For a small reel and wanting to throw slugs the higher gear wil definitely be better. We saw this last trip using a Stella 5000 and a Symetre 4000. The Stella was all over the Tuna with the 6.2:1 retrieve.
Also, it seems hard to justify the extra dollars for the Sustain over the Stradic as it is such a nice reel itself. I can't remember the gear ratio of the Stradic compared to the Sustain though.
A left field option would be the Shimano Aceration. It's a high geared JDM version of the Saragosa which makes it attractive for salt water use. I've not used the new Stradics as I didn't like their corrosion resistance in the older models. They might be better though.
I can't comment on the Biomaster but if it's the SW version it will be a very good reel as it is above the Saragosa in that line.