I'm thinking about buying an SSD for my laptop. I can get the 750evo for 125€ and the 850evo for 165€. Are those extra 40€ worth it? And what are the advantages of the 850 over the 750?
Pretty much boils down to the life cycle/durability of the MLC cells, i believe the 750 is made from some cheaper cells which degrades it's mean number of write cycles pr. cell, and also not uses the 3d cell technology, which lower the maximum size of them e.g. you won't see a 16TB version anytime soon, but this also lowers the production cost.
Performance wise they're fairly close the 850 having faster write times though, but it's nothing you'll notice much once your system is running, since it's like comparing ridiculous fast to just regular fast.
Just like Lauritzen said everything boils down to how much to you evaluate a more resiliant NAND. I think those 40$ more required for the 850 Evo will pay off in the really really long time so if you're going to get better storage anyway before getting the drive to it's knees just go for the 750.
The 750 is significantly less durable and is also quite a bit slower than the 850. I would go with the 850 if you can afford it, but both should still be decent in day to day usage.