The 25s (expensive ones not the SPs) were my travel headphones for planes and trains. I have happily replaced them with the X5s. The X5s have better isolation and the sound quality is on a par. I would say that the 25s are more neutral whereas the X5s are a little more pop EQ. They are a bit boosted in the upper bass (around where the bass guitar would normally play) so they have a "warm" sound. The X5s are fun and satisfying to listen to. However on the negative side the cables are quite microphonic if you are moving around - an issue with all the IEMs I've used. And you can't take them off (out) as easily as an over the ear headphone like the SP25s.
The 280s have better sound isolation than the 25s (on my head anyway) but the Klipsch probably have the edge on that and also look less dorkish than the 280s. I use 280s quite often for mixing live sound (bands at gigs) and would always prefer the 25s for that purpose because I feel that the 280s are too bass light. If I'm soloing the kick drum or bass guitar I always seem to need to turn up the headphone volume on the mixer to get the definition and volume I require with the 280s, whereas the 25s are more even in their frequency response. What I guess I'm saying is that the 280s bass response is a bit rolled off, even from a mains powered headphone amp.
This link below may link to a graph that shows that although the 280s have a bit of bass boost there is a distinct dip around 80 Hz which is the part of the frequency spectrum where the fundamental note of a kick drum normally lives. That may explain it
http://graphs.headphone.com/graphCompare.php?graphType=0&graphID[]=533&graphID[]=513&graphID[]=2271&graphID[]=753
I haven't heard the new Senn 380s which should be an improvement on the 280s.
Sorry to waffle. It would be good if you could listen to some X5s or X10s yourself before laying out the cash. I bought mine from a little stall in the airport at Minneapolis-St.Paul, which let you demo all of their headphones including the in-ears (they had spare earpieces). Very handy.
Andrew