Got a Crucial m4 256GB SSD in a 2011 Mac Mini. It's been in there for years but for the past year or so I've had consistent shockingly bad speeds: max 50mb/s write, ~75mb/s read. I've had TRIM off since Yosemite or whichever OS it was that disabled third party TRIM support. Upgraded to El Cap and used the "sudo trimforce enable" command in Terminal. Deleted a few unused apps totalling 5-6GB, waited a few mins, ran a blackmagic speed test again and bam! 265mb/s write, 498mb/s read. Far cry from the newer Apple PCIe SSD speeds but much happier considering my older speeds. I read about degraded performance over time without TRIM but 75mb/s read to almost 500!? I honestly thought my machine was just getting old, didn't know a simple command could bring it back to life. Hopefully this helps someone else with poor speeds on the fence about enabling TRIM.