OEM drive...doesn't it also have a different model number than the retail drive (SM841)? So you didn't buy a 840 Pro but a SM841.
OEM drives don't support firmware updates. The OEM manufacturer has to provide it, which almost never happens. Also you cannot use the Samsung Magician software which includes the amazing rapid caching mode.
Well not really, they are OEM drives, and my take is that they are cheaper and have a shorter warranty for a reason. I think their flash could be cheaper (sych instead of toggle flash) flash or binned lower than the retail drives. I can't prove this but you have to ask yourself why they are sold on the grey market with a 20th of the warranty (.5 of a year instead of 10 years).
256GB DELL SM841:
READ MB/s Write MB/s
SEQ ........... 524.2 504.0
512K .......... 484.5 490.6
4K .............. 37.57 70.14
4K
QD32 ......... 252.4 234.7
256GB RETAIL BOX 840 PRO
READ MB/s Write MB/s
SEQ ........... 499.1 506.6
512K .......... 465.1 492.1
4K .............. 30.47 66.41
4K
QD32 ......... 226.0 202.6
They are 100% identical except for the firmware, it's just the OEM version they sell to Dell, which is why it only has a 6 month warranty, because if the drive is inside a Dell laptop you have the Dell warranty of how many ever years.
When the software SAMSUNG MAGICIAN is used to tweak the OS, YES IT DOES inflate performance a LOT, but that’s cheating, especially with Rapid Mode it’s not really bench testing the SSD, it’s cashing system RAM. IF Samsung Magician worked with OEM firmware, the scores would be the same for either drive.
Don't worry I didn't just buy it on a whim, I did my research.