Just replaced my 2 256GB Samsung 830 SSDs with these 2 new 256GB Samsung 840 Pro setup as Raid 0 for a total of 512GB.
The 840s are a tiny bit faster in terms of read speeds. 540 MB/s for the 840 Pro, compared to 520 MB/s. and over 20% faster write speeds, 520 MB/s compared to the old 400 MB/s
If it wasn’t for the fact that I had to get my hands on the latest and greatest, and also keep in mind that in both scenarios, I had 2 of each models set up as Raid 0, I did not see any real life performance gains, upgrading from the 830 to the high and almighty 840 Pro, did not magically make my Windows 8 boot time decrease from 10 seconds to 8 seconds! Also, it did not make Starcraft 2 load 50 times faster! However, you can definitely see the difference in benchmarks. But then again, upgrading from a very fast SSD to an even faster SSD must be all about the benchmarks 😉
If you are coming from the good ol’ HDD then I would definitely recommend getting the 840 Pro. Otherwise, if you already have the 830 model, you gotta ask yourself, is it worth spending the extra money to see improvements in benchmark numbers only?