One of the great features that the new Android 4.3 Jelly Bean operating system was made available with is TRIM support, which should result in improved overall performance of Nexus devices, regardless of their age.
As AnandTech notes in a recent article, TRIM essentially enables the OS to “inform” the SSD or eMMC controller what blocks are no longer in use, thus preventing it from tracking that data even after it has been deleted.
The controller will then schedule said blocks for garbage collection / recycling, which should result in improved performance of the device. Basically, faster speeds will be seen on devices updated to Android 4.3 only after the OS has had the chance to run TRIM for the first time.
Android 4.3 Jelly Bean has been constructed so as to invoke TRIM maintenance once every 24 hours, but only after one hour of inactivity and only if the battery is at least at 80 percent (or 39 percent when charging).