I'm choosing a 240GB SSD for my old 2011 iMac which has SATA2. Does having SATA2 mean I don't really need to worry about getting the best high end SSD (Samsung 850) as I won't be able to get the high end performance benefits anyway?
You won't necessarily benefit from the fastest speed, but buying a decent ssd may still have some longevity benefits. Also Apple don't enable trim for SSDs by default with the exception of Intel and Samsung drives from memory so buying an Intel or Samsung drive saves you some command line hacking to force trim on.
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