We briefly had an E series drive to test, and it does fragment (by about the same ratio seen on the M drive), but it immediately snaps back, just as the M series drive does most of the time. We only had the drive for a week so we were not able to find out if it hits the 'point of no return' we saw with the X25-M.
Keep in mind this fragmentation is really just a down side to write combining. It is a simple tradeoff. The X25 drives achieve crazy high small write IOPS using this technique, in fact the M even beats out other SLC drives in this very area. If you do nothing but hit it with small writes, it is eventually going to slow to the point where it acts more like a non-write-combining drive, and larger writes will take a hit because of the fragmentation that came about from the initial write combining. Hitting it with a mix puts the average write speed at some point between 40 and 80 MB/sec, all depending on the particular mix of large and small files written (i.e. your usage pattern).
Even after writing the article, I still use my X25-M as my primary OS drive, even with all of the other SSD's at my disposal (including SLC units). Its insanely high IOPS performance makes it the best choice. You just have to realize that hitting it with a constant power user workload will slow it down. It is *supposed* to bounce back with larger writes, and we are working with Intel so they can easily replicate the 'bad' cases we saw. I suspect that once the Intel techs can dissect what we stumbled on, that a simple firmware fix will solve that particular issue.
A side note: Some sites have taken the Intel statement and spun it as if the drive does not slow down at all. This is not accurate, and I believe does everyone a disservice. Intel and PCPer have a mutual understanding that usage will drop performance to a steady state value based on that usage. You have only to read the "Ask and Intel SSD Engineer
" article on [H] Enthusiast to figure that much out... It is also worth mentioning that the official write speed spec of the X25-M is 70 MB/sec, where a 'new' drive will write at 80/sec (closer to 90/sec with AHCI enabled). Clearly Intel considered this slow down when they published the spec, and it was very honest of them to do so.