geofelt :
All current ssd's have essentially the same performance.
Even the m.2 which has a theoretical advantage in sequential speed is probably not much worth it.
The big advantage of a ssd is the random I/O service times and that differs little.
Buy the cheaper option, especially if it comes with a similar warranty.
If you have a choice, opt for a larger ssd. They tend to perform a bit better.
geofelt - i hate to differ but i had a xp941 256 gb in my desktop last week for a few days, in the M.2 socket with only two PCI3 lanes, and it was light years faster than my samsung 840 256 gb SSD - the 840 isn't but 4 months old and i've got the samsung performance restoration software installed.
the rest of the system: i7-4790 (locked), asus z97m-plus mobo, 16 gb 1600 Mhz ddr3 ram
Boot time (cold) went from 20-22 seconds to 10-12 seconds. Programs like adobe photoshop that normally takes 5-8 seconds to open, dropped to 2-3 seconds. Quickbooks, similiar drop in time to open
small video files that took 10-15 minutes to render dropped to 5-6 minutes. I didn't do actual file comparisons, I just knew the type and size file i was rendering normally run 10-15 minutes, and i did time a couple with the xp941
the actual "feel it, see it" speed is there