I would use both of the slashes (rending and poison). As for the spammable, I currently find that crushing weapon from the psijic line is better than flurry, but once the new version of fllurry goes live that might change.
Flurry is fine too. And crushing is arguably a little but less good than the magic version (elemental) but I still get good results from crushing, at least on my StamDK and StamSorc.
I would use both of the slashes (rending and poison). As for the spammable, I currently find that crushing weapon from the psijic line is better than flurry, but once the new version of fllurry goes live that might change.