These 3 OCZ drives appear to all be SATA III and of a similar capacity, so can anyone explain exactly what the differences are and whether it's worth paying the extra over the cost of the Agility model please?
Listed in ascending price order:
OCZ Agility 3 120GB 2.5" SATA-III
OCZ Octane 128GB 2.5" SATA-III (does this have the older controler?)
OCZ Vertex 3 120GB 2.5" SATA-III
If I were you I would get the Crucial M4. I realize that isn't your question but I believe if you are going to get an SSD, you should get the best reliable one that is at a good price. As for your question, than nityking has it.
The following are all SF controllers and are the main lineup of drives:
Solid3 is their entry level drive (works quite well though. I purchased this for my wife's older PC)
Agility3 is their mainstream drive
Vertex3 is their performance drive (this is what I am looking at down the road)
Vertex3 Max IOPS Edition is their enthusiest drive
Considering how fast the entry level drive is with a mere C2Duo, it is still hard to imagine how fast the vertex will be in a more modern system
you are right about Octane, it is not quite up to snuff yet, but it looks promising (or at least interesting) for future releases and updates. It is a very young product and OCZ's first attempt at making their own firmware, so I would avoid it. Also judge a SSD by it's IOPS rating, not it's MB/s. You do not buy one to get more MB/s (though it is a nice perk), you buy it for the 0ms seek time, and how many operations it can do per second.
The OCZ worry is mostly from a rocky start on the Sand Force 2xxx controller firmware, but the issues have been dealt with and they are perfectly good and working drives. The M4 has some advantages, like not relying on TRIM support, better automated garbage cleanup, and some other things, but for 90% of us there is little to no practical difference between them, and the OCZ is a little faster for less $$.
As I said, I have an OCZ on my wife's PC and it works very well. The only problem we have had with it is that occasionally (once every month or so) the system will hang when going into sleep mode. Considering it goes to sleep about 5-6 times a day I am not all that worried about having an issue once every month or so, and a hard restart fixes the problem.