Intel currently lists two models in the 311 Series of products. Both have 20GB of capacity and use single-level cell flash, the same used in many expensive enterprise SSDs. Both the 2.5" and mSATA 311 Series drives are rated at 200MB/s read and 105MB/s write speeds with a read IOPS rating of 37,000 and a write IOPS rating of 3,300. The performance numbers don't look all that impressive, especially when compared to new SATA III drives like the Intel 510 Series, but there are some things to keep in mind before throwing stones.
In the past we've shown that multi-level cell SSDs slow considerably when data is present on the drive. Data being on the drive affects MLC SSDs more than it does SLC SSDs. Since you want your cache drive to hold as much data is possible, your SSD cache drive will be filled to 100% of capacity nearly all of the time.
In testing we've also observed that data is often swapped in and out of the cache SSD; this is a smart system with some intelligence after all. Frequent random writes are an enemy of MLC SSDs and you have a limited number of writes before you run out and lose the ability to write to a page in the flash.
SLC has a much higher endurance rating and that is a big reason why Intel chose to use SLC flash in their 311 Series.
The Intel 311 Series 20GB mSATA drive packs quite a bit in a small package. At about the same size as a notebook WiFi card, the 311 mSATA is perfect for notebooks and onboard desktop motherboards. We've already seen some notebooks with mSATA ports and the number is growing. Newegg lists the mSATA 311 Series at 119.99 at the time of writing.
It's important to note that even though the GIGABYTE GA-Z68XP-UD3-iSSD includes a mSATA Intel 311 Series drive that it can be used in future builds. This will depend on GIGABYTE releasing more products with a mSATA port on the motherboard for desktop use, or your ability to install the drive in a notebook later on when purchased.
The 2.5" Intel 311 Series drive looks like any 2.5" SSD selling today and uses a SATA port for connectivity. SATA is the universal standard for storage drives these days and your upgrade options are less limited than they are with an mSATA drive. Newegg lists the 2.5" Intel 311 Series at 114.99.
The initial cost difference between the two 311 Series SSDs is quite small, around 5 Dollars. This is if the drives are sold separately and not bundled with another product. The best deal initially is the GIGABYTE GA-Z68XP-UD3-iSSD that ships with the mSATA SSD. The price premium for the -iSSD is less around 90 Dollars when compared to the non-iSSD model. This is less than the 120 Dollars it costs to buy either of the Intel 311 Series SSDs.
Even though it costs more from the start, the 311 Series 2.5" drive may be a better choice for someone looking to upgrade every year or every other year. With the mSATA 311 you are depending on motherboard companies to release future products with mSATA onboard and there are no guarantees it'll happen.