Fun stuff ahead. It's interesting to note that slash users get more bang for the buck per realm point than pierce users. Since slash is str only, you can purchase aug str 5 and get a huge boost to your weaponskill. Pierce users would have to purchase aug str 5 & aug dex 5 to get the same weaponskill boost.

It never mattered as much before because we all tended to get aug str & aug dex for the pre-reqs.. it might actually be noticable now.

If things don't change (they will). As a slash user I'd currently go either (with 55 pts):

Aug Str 5 - 34 pts (+48 str)
Purge 2 (a must) - 15pts
Vanish 1 - 5pts
MoStealth 1 - 1pt

or

Aug Str 3 - 10 pts (+22 str)
MoP 3 - 10 pts
Purge 2 - 15 pts
Vanish 2 - 15 pts
Whirl Derv 1 - 5 pts

Others to consider:
Aug Con.. hmm, maybe not.. want to kill fast and vanish, not last longer.

Avoidence of Magic.. would love to have to help counter fire/energy weapons.. not sure if stealth vs stealth game is a thing of the past now with vanish tho.

2nd Wind.. full endurance is always good, but pots and other RA's seem better choice.

Empty Mind.. great for same reasons as Avoidence of Magic.

Viper.. not so sure about, any below RR5 nightshade I won't need the bonus, and above RR5 nightshade will be able to counter poisons.. everybody will have purge twice as often.. vanish will be a purge alternative. All this adds up to poisons being less effective. Will even consider respeccing to 50 slash/ 50 crit/ 34 stealth/ 34 dual wield.