thanks for this info, but what about my question of whether the drive being OEM and having the different firmware means it's "better adapted" to Lenovo computers. Is there any truth to this?
yes, there absolutely is truth to that. any SSDs included from the factory in any manufacturer's system will contain firmware tweaked especially for their systems. typically this is to cover compatibility or reliability concerns. the same goes for spinning hard drives as you'll find certain features disabled in the firmware (ie: timeouts to allow RAID use with a desktop drive, accelerometers disabled in notebook drives, etc.).
the other difference is support. getting a replacement drive from intel is a $25 fee to pre-ship a replacement, otherwise it's a good 2-3 weeks to ship your drive and await the replacement. lenovo on the other hand will have a replacement in your hands the next business day at no charge provided your system is under warranty. buying an SSD with a thinkpad can be slightly more expensive but the added cost is worth it to business and enterprise users who need quick replacements in the rare event of a failure.
regarding SATA II versus SATA III, choose based on reliability. you won't likely be able to discern a difference between the two in real-world use unless your workload mostly comprises large file transfers. even then the difference is negligible outside of benchmarks.