Have both the SA6s and the X10s, and I really like them both. X2 on the post above, but I would not say it's so clear cut that the SA6 has the advantage over the X10s apart from bass and comfort. Without an amp, I do rate the SA6s a bit higher, but with the LOD on my Touch with the MiniboxE+, then I prefer the X10s (they respond to amping much better).
Of course, in terms of price, the X10s are more then $100 above the Sleeks (if you buy both from authorized dealers).
Finally, on the durability front, I have had two sets of drivers replaced by Sleek (which has excellent customer service, as you have no doubt read), once for a small cosmetic problem, the other time when one of the drivers stopped delivering sound. And that is in about 6 mos. time. Michael at Soundearphones.com says that Sleek has fixed those durability problems, but I have no way of knowing if that is the case.
The X10s are a single piece, and doubtful they will break considering how small, light they are. I mean they have very little to break externally in terms of pieces, compared to the Sleek modular system.
Both carry a two-year warranty.
Finally, don't discount the comfort factor. I use foam tips with the Sleeks (Shure olive or yellow standard), and while they are fine once you get them in the right spot, it takes some effort. With the X10s, 3 seconds and they are where they belong (I use the supplied bi-flanges, large, and believe they are by far the best Image sleeves).
Can't discuss the X5s, never owned them.
Realize this doesn't tell you which one to buy, but hope the details help with the decision.