I would go with
Crucial M4 instead. Agility 3 is a SandForce based drive and hence not really known for reliability. Plus the Crucial is actually slightly cheaper.
Couple of thing: That drive is only 64GB. After over-provisioning and OS X install, you would most likely have around 50GB of free space. That's very little given that it would be your primary storage. I would get at least 128GB.
Moreover, Patriot drives are very hit&miss. That specific drive uses Phison controller and to be honest, this is the first time I've seen that name. It promises decent speeds but it may also mean incompatibility and poor reliability. I would stick with known controllers.
Serial ATA (or usually just SATA) is the interface used by most internal hard drives and SSDs. The difference between SATA 3Gb/s and SATA 6Gb/s is their speed: SATA 3Gb/s is good for up to 3 Gigabits per second while SATA 6Gb/s is good for up to 6 Gigabits per second. When 8b/10b encoding is taken into account, we are looking at ~280MB/s and ~580MB/s in real world.
In a nutshell, SATA 6Gb/s is twice as fast as SATA 3Gb/s, However, keep in mind that the actual bandwidth is determined by the SSD and its controller, NAND configuration etc. SATA 6Gb/s SSD is not automatically twice as fast as SATA 3Gb/s SSD.
I've said this before but SSD is the biggest upgrade you can make today. It's not just marketing speech, it really makes a difference. How much it's worth is another question, though. I would look into the Optibay solution as 512GB SSDs are really expensive. Optibay allows you to have both SSD and HD inside your MBP at the expense of the optical drive. That way even a 128GB SSD should be more than fine, which cuts the cost a lot.