I am building a system and want an SSD for my boot drive. I want something super fast and was planning on getting a 64GB X-25 E but looking at the specs the X-25 M has the same sequential read speed. The X-25 E has a faster write speed but I don't think that matters when using exclusively as a boot drive. So is there any advantage to spending the extra money for the Extreme?
I think you'll find the M drive to be just fine. The most critical performance metric for general-purpose use is random read I/Os per second, write performance is almost a complete non-issue unless you plan to use the drive to frequently write large files to. In that event the higher write speed and better wear characteristics of the Extreme drive would be a benefit.
I know I'd want to at least know about them if I was just about to buy a new SSD...
Especially the 256GB varient will be quite a bit faster than Intel's offerings.
The 128GB version (not in reviews) has a slightly slower write s[eed at only 140ish MB/s (still faster than Intel) instead of 215MB/s
The next generation "E" (extreme) Intel SSD will be based on MLC NAND flash, like the "M" versions are. Benchmarks also show the X25-M G2 to be faster in some benchmarks than X25-E, so Intel proven that MLC NAND flash can be used in high-performance SSDs as well.
Of course, SLC provides other benefits like longer lifetime in write-heavy situations. Except for extreme scenario's, at this time there is not much reason to buy X25-E now that X25-M G2 is out. Next generation Intel SSD ("Lyndonville") will take advantage of SATA 6Gbps and command buffering.
What the Extreme series stand out for, is their lower capacity due to alot of the raw capacity being reserved to speed up random writes. The M series has less space reserved so its a trade-off between capacity/price-per-GB and performance. But it appears even the E series will be using MLC NAND flash memory when the next wave of Intel SSD's present itself.
Sub mesa - where are you getting the info that the next gen X25-E will be MLC? That seems unlikely to me, since the E is meant at least partially as a server drive, in which the extra write reliability of the SLC would be extremely beneficial, and price is not a significant concern (compared to a normal user drive)