Who knows? OCZ usually comes out with a zillion similar products. Originally with the Indilinx controller the Vertex was the "premium" line using guaranteed certain brand of premium NAND, while the Agility used cheaper NAND that was supposedly a hair slower (by "hair" I mean maybe 2% or less). Then they came out with the Solid 2 using the same controller but even cheaper for unknown reasons. And then they mucked it all up because sometimes the Vertex was cheaper than the other two. Then they came out with an overclocked Vertex (indilinx controller running at a faster speed) which added another 2% performance at 20% price premium.
Think of it like all the different lines of RAM modules that OCZ releases. When you say that you have OCZ DDR2-800 memory, do you have their Gold, Platinum, Reaper, Fatal1ty, Vista or Value series? And, if the specs (voltages, latencies) are the same, what is the real difference?