You'll notice that that link recommends a PSU 100 watts more powerful than what Nvidia recommends on their website. This is because the manufacturer usually states the minimum power required to run the car,. A GPU at max load draws considerably more power.
Your PSU should be fine. Just don't connect a tonne of hard drives simultaneously.
The Silentium product has a better range of connectors attached to the PSU. I'd choose that.
Bear in mind however, that the Wattage on the Silentium is insufficient to power a GPU that might need all the connectors it provides. However, the Stealth is no more powerful, so I'd choose the Silentium.