In order to use trim, you need to use a kernel that is 2.6.33+ and ext4 mounted with the "discard" option. (TRIM won't work unless you have all 3)
To overprovision, simply partition the drive using 80% of the unallocated space.
You won't need to set aside any area on your 710 SSD for over-provisioning. The 710 is designed for the enterprise environment, and Intel has over-provisioned the 710 by design.
A review of the 200GB version of the 710 examined the NAND chips inside it, which are labeled and so their capacity can be easily determined. The 200GB 710 contains 20, 16GB NAND storage chips for an actual capacity of 320GB. It's more than likely that the 100GB 710 SSD contains 10 of the 16GB NAND chips, for a total of 160GB. So your 100GB 710 has 60GB of spare, over-provisioned area now.