I'm a big fan of the X5s. After one was stolen and another died, I had to go to the X10 series.
I have both the X10 and X10i. Big price difference. The only difference in features is the volume slider on the X10i. You'll appreciate the slider when using an iPod.
I still prefer the SQ of the X5s. The X5s also are a bit larger and they fit my ears even better than the smaller 10 series. The 5s also seem slightly less fragile, although it's hard to tell for sure.
I wish Klipsch would bring back the X5s, which were cheaper and every bit as good, IMO. Perhaps they were too much competition for their more-expensive stablemate.
That said, I'm thankful that Klipsch continues to produce an X series. After my 5s went missing, I spent too much $$ trying out other brands without success. I even tried to use Klipsch's oval tips with the other brands. No deal.
Are the X10 series worth the full list price? Only if you have cash to burn. I've yet to come across any earphones that are worth that much to me.
On sale, that's different. I wish i could afford to stack up a bunch in my closet.