Not taking the reputation and quality of different brands (OCZ, Intel, etc.) into consideration, is there a major benefit of Sata III 3.0 vs. 6.0 as long as the drive is a Sata III drive?
Don't get it confused, there's no such thing as a SATA III 3.0 drive.
SATA II aka 3.0 has a theoretical bandwidth of 300mbs. (second generation)
SATA III aka 6.0 has a theoretical bandwidth of 600mbs. (third generation)
Only a SSD SATA III drive (600 mbs) can peak the bandwidth a SATA II port provides (300 mbs). Unless you are monitoring read/write speeds or running benchmarks you won't notice the difference. A couple months ago I went from an older G.Skill 120GB SATA II SSD to a Crucial 128GB M4 SATA III SSD and I can honestly say unless I'm running benchmarks or monitoring read/write speeds I don't notice the difference.
I only run the OS and apps off the SSD either way, not like I move gigs of data to it and from it to notice the diff.