gen 2 is for recommended for Mac because the Mac pros are pci-e 2.0 and you will get better performance using Squid PCI Express Gen 2 Carrier Board on a Mac pro but if you have a hackintosh that use pci-e 3.0 then you get the maximum speed using Squid PCI Express Gen 3 Carrier Board
is not that Squid PCI Express Gen 2 is faster than Squid PCI Express Gen 3
is just that version 2 runs better on a Mac Pro
version 3 is definitely faster but it won't work as good as version 2 on a mac pro because the pci-e 2.0 bus speed
but on a hackintosh a version 3 will smoke and blow a version 2 out of the water
as long as that hackintosh has a 16X pci-e 3.0 slot
this is the new card but it is for Mac Pro 2013
http://amfeltec.com/products/mac-pro-late-2013-carrier-board-for-m-2-pcie-ssd-modules/