I've never run a Raptor unstriped, so personally, I don't know the difference between a single drive and a striped drive when gaming, for example. I'm not uncomfortable w/ a RAID 0 setup and OK w/ the seemingly negligible performance increase when using a striped array. As far as data loss, I backup my OS on an external drive and an independent internal drive on a nightly basis. Overkill? Perhaps. However, I'm aware of the risk that this type of setup presents, and it doesn't hurt to be "too careful."
SLI is another story. With the original cost of the GTX, plus the cost to step up to the Ultra, I paid over $700 for a setup that is currently performing worse than the SLi'd GTXes. Basically, I feel like I !$%*ed myself. Everything I've read (from reliable sources) suggests SLi is not worth the cost. From what I understand, SLi is only beneficial when running resolutions above 1920 X 1200. <- Even that's debatable.