How to comprehensively benchmark SSDs on OS X?
For the OP, look up fio, I think someone mentioned it somewhere on this. It's the best way to explore the limits of the SSD on your Mac. Just be sure to use the 'direct=0' argument, or you may bork your filesystem. 

That said...

Some of the answers here are just absurd! I know the replies are years old at this point, but you absolutely can, and SHOULD, measure IO Latency of an SSD. 

tl;dr: SSDs have IO latency like any other storage system, you can measure it. 

There's a distinct difference between 'Seek Time', a mechanically-bound metric associated with spinning disk, and 'IO Service Time' which is an aggregate of the latency associated with each step of the I/O process. In environments with spinning disks (including home PCs and Macs), Seek Time is one such step, and can be quite significant in poorly designed/cached/maintained systems (which is probably the vast majority of business systems, and nearly every home system not run by someone skilled in the realm of storage performance tuning).

Generally, folks are referring to this IO Service Time when they say 'latency', and not 'Seek Time', as that metric has become increasingly irrelevant as:


Flash-based storage devices become the norm
Spinning disks inside and outside of the enterprise IT shop bump up against mechanical limitations which simply cannot be exceeded due to physics
Systems needing real performance rely on software optimizations (caching implementations, IO coalescing, maintenance of stripe sets and other tricks to ease the grip Newtonian physics has on the storage system's disks) or expectation management ("If you want faster, don't be cheap, buy flash, otherwise hush.") as most of the ultra-high-performance storage consumers have moved to Flash long ago, taking the pressure off of spinning disk manufacturers to push for that last quarter of a millisecond of seek time performance


When we are evaluating a storage system, we are talking in terms of microseconds most of the time. These days, if a storage system cannot provide consistently sub-5ms performance under any load (for general workloads), it can't hang. For the high performance consumers, we expect consistent sub-1ms response times for the critical workload profiles. 

The fastest spinning disks you can get have seek times of over 2ms alone, and that's the best case scenario. Add in the fact that if you're in a RAID array scenario, every disk needs to seek to the desired stripe and they may be all over the place as far as head position, so it can get pretty ugly. (In a pure hardware RAID scenario without caching strategies to lessen this, see above.) Add in to that the time it actually takes to move the desired data, compute parity if necessary, update stripes where applicable... You can see, the benefits of SSDs become obvious immediately, in terms that aren't very hard to articulate, once you know what's up. Hope this rant helps googlers out there in their quest for the knowledges.