Reason to buy the intel 320 or 520 drives? RELIABILITY. Check Newegg and other online complaints... constant BSOD, performance drops, TRIM not available or working right, out-right failure... especially from OCZ. I've set up X25M in many systems without a hitch. And in some benchmarks, especially random - the X25M still holds its own.
I just built two systems with the 320 in one and the 520 in the other, otherwise same mobo Z68 Mobo and i5-2500K CPU. Both booted into Win7 in about 24 seconds (power on) / 11Sec after POST. Run a benchmark afterwards and the 520 is much faster in many categories, but not much better than the 320 in random read... but the i520 can do everything with much less CPU utilization. (0~4%) compared to the i320's 4~35%!
Intel has excellent SDD tools... which OCZ doesn't have, period. I worked on a rather new system with an OCZ, went to their site for utility tools... nothing.
Intel also includes a 3.5" bracket and cables (okay $5~10 worth of goods), a CD and a big-ass sticker that says Speed Demon. The removable plastic retainer is handy for different size drive bays. (intel doesn't include smaller screws when its removed... scotch tape works)
In the store I bought the latest SSDs, they have a basket full of 128GB $110 OCZ Petrol drives in cheap plastic... I don't think anyone would bother to steal them. (The intels are in a cage) - Yep, I'd take the $200 i320 SATA II over the $110 SATA 3 OCZ Petrol... the reviews for that drive are bad... very very slow drives with very fast failure rates. Lots of DOA and lots of deaths 1~50 days of use.
OCZ, trying to make a few bucks selling cheap drives ends up crapping on their own brand name. Something intel and Samsung try very hard to NOT do.... making crap is a way to drive away customers.
Intel drives, not the very fastest... but 5year support, minimal failure makes them worth every penny.
Read the horror stories on newegg.