This is my take on this as it has become a touchy topic. I own a lot of M4s and so I have been reading up on this. As of now, there is no conclusion on which is better, as many respectable people have very different views.
The Crucial uses garbage collection that works when the drive is mostly idle. TRIM works as an 'on the fly' cleanup, in that it is active. I believe SandForce drives via Durawrite do this too. Crucial says that the drive's own garbage collection is sufficient, others say it is not. This seems to indicate that enabling TRIM may be determined by who uses their drive how heavily. I have been benchmarking all of my Crucials, including my C300. As of right now, none of them have had any slow downs. Even our original 64 GB Apple SSD in the MBA still runs almost as fast (and has had virtually no size reduction). So at least for what I do with most of my computers, I do not currently need TRIM. On my MBP, I write-rewrite about a GB of data a day, give or take. And so I benchmarked it immediately after install, and have been benching it weekly to look for any signs of slowdowns. It's only been a few weeks on this one though and so I can't say much about it. My MBP sits idle overnight and so I am not expecting a slowdown. Also, I believe you can manually restore the Crucial's functioning if you move a large file, such as a movie, and then delete it. Literature has shown that while you can cause the Crucial's write speeds to slow, once the drive sits idle, it fully recovers.
As of right now, I believe that the Crucial's garbage collection is sufficient. Some people go as far to say that it is not only sufficient for non-TRIM OS', but actually ideal. As we know, the Crucial has a Marvell controller in it. Some writers have stated the Marvell to be the best for non-TRIM environments (even better than the Sandforce ones) as they claim the Marvell was designed with the assumption that TRIM would NOT be available where as other controllers were designed with the assumption that TRIM would be available and always utilized.
see:
http://www.hardwarecanucks.com/foru...iews/45718-crucial-m4-256gb-ssd-review-2.html
In non-TRIM environment testing, the M4 does very well. In fact, it spanks the Sandforce drives, which may explain why my M4 seems to do a bit better in the real world than my SF ones for running OS X.
see:
http://www.hardwarecanucks.com/foru...ews/45718-crucial-m4-256gb-ssd-review-12.html
So what does that mean to users? My take is that some users may need active garbage collection if they continually move data about and have few or no periods of inactivity for the drive to cover. My take is also that most users should be okay without TRIM. While it seems safe to enable TRIM for the most part, I have read a few reports of bad things happening when doing so. Because of all of this, I personally am not going to consider enabling TRIM unless I see a slowdown of the drive. If that slowdown never comes, I personally do not see a need for it at this PIT. However, your needs may vary.
Finally, if we want more conclusive evidence, we could get data from RAIDed systems using Marvell controllers because IIRC TRIM can't be used in a RAID config. IIRC some of the Intels are Marvell. If the X25M is a Marvell controller, then this data may exist as that seems to be the common SSD used at the enterprise level currently.