I'd suggest taking another look at Vanquishers sword, it's an amazing offhand for warriors.
Numbers assume 0 in dw spec.
WSG sword has 13 higher average damage than vanq, divide by 2 for being in the offhand that's 0.65 less whirlwind dps if you are whirlwinding on cooldown, or 0.8125 dps with glyph.
Vanq has 12 more attack power. That's 0.88 more dps on the mainhand, 0.43 more dps on the offhand, total of 1.31, times your chance to hit (i.e .76 with 0 +hit). That attack power also adds 3.144 damage to your average whirlwind, for another .3144 dps, .393 glyphed. The weapon dps itself is .7 higher, halved for offhand again, another .35.
In a scenario that is best for wsg sword and worst for vanq (WW glyph, 0 hit rating, 0 in dual wield spec), vanquisher allows you to deal .9261 more dps.
The difference in burst damage (higher whirlwinds with wsg sword) is less than 3.5, although it varies higher when you include a white offhand hit.
When looking purely at damage output, the vanquisher sword is simply superior. I'm not sure whether you favor wsg sword due to the increased burst, or the extra stamina, but completely neglecting to include what is probably the best offhand in the bracket for overall damage output is a real disservice.