Ok thanks for the feedback I'm new to Sin so I wasn't sure if Wither was all that good. But it seems it is.
Now I have another question: Can I take Deathfield instead of Wither for the self heal? (simply asking. Again new to Sin)
For pve, you definitely want wither. However, a lot of people pick up death field for pvp, although not for the self heal. 23/1/17, up to instant whirlwind is quite strong, and the utility makes it one of the better assassin builds for rateds, not to mention a decent choice while you are gearing up. That said, if self heals are a priority for you, this obviously isn't the way to go.