Sorry for thread necro, but this seems like the best place to post this since I have some questions about this exact spec (DW rogue Tempest).
For weapons, do you prefer crit chance or crit damage? I was about to make a Coiled Strike with crit damage, but then I realized I could throw full (12 Great Bear Hide) crit chance on two daggers and completely ignore needing crit chance anywhere else (43 + 23 + 23 = 89% crit chance from weapons and passive while flanking.. passive skills should push me over 90% via cunning and for a single player game I really don't care to bother with hitting 100%). This also has the (very minor) benefit of being able to throw full dex into utility slots to take advantage of crit damage + attack, since I don't find ranged defense from cunning very useful.
Also, for people advocating Poisoned Weapons.. why? It takes up a precious ability slot, which this build is extremely hungry for. There is barely any room to fit a focus ability, and PW is extremely underwhelming. 500% over 10 seconds.. most non-dragon enemies won't survive long enough to eat the full effect of that (even on nightmare), and flying around the battlefield poking everything to poison them is very inefficient. PW just seems like it's better on a ranged character since because of cooldowns you're going to be auto-attack quite a bit anyways. You can fling an arrow at every enemy and then just focus on whatever afterwards.
As far as stealth, aside from using it to drop threat, I don't see it as especially useful here. Most enemies you'd care for the extra damage against can perceive you through stealth anyways, and the 50% bonus only applies to one attack. What would be interesting is if the bonus applies to EVERY hit of Thousand Cuts, and not just the first one. That would make it very devastating.
UPDATE: Just did testing on this. The results are very underwhelming. You stay in stealth the entire time you use Thousand Cuts (and in fact, using Thousand Cuts doesn't even break stealth), but it either doesn't work with Thousand Cuts or the stealth bonus is additive to other +damage bonuses you have (meaning it doesn't actually increase your overall damage done by 50%, as I thought it would).
Non-stealth hits: ~600 non-crit, ~1700 crit
Stealth hits: ~600-700 non-crit, ~1800-1900 crit
A small increase in damage, but it was very inconsistent for some reason.
Hmm.. I just realized that Ambush requires stealth though.. that's something I guess. Armor penetration isn't that important for most enemies though. Looking at combat mechanics, armor penetration for high attack speed characters actually scales ridiculously well in this game against high armored targets, so it looks like a strong consideration against dragons. Probably only for Thousand Cuts though, trying to remain in stealth is impractical in most cases I think.
EDIT: Also, seems like I may have discovered a weird critical damage bonus cap. My +49% critical damage dagger is only adding +25%, for a total of 178%.