Yapt (yet another performance test) is a benchmark recommended by a pair of drive manufacturers and was incredibly difficult to locate as it hasn't been updated or used in quite some time. That doesn't make it irrelevant by any means though, as the benchmark is quite useful. It creates a test file of about 100 MB in size and runs both random and sequential read and write tests with it while changing the data I/O size in the process. The results are a good look at overall drive performance.
The 840 did well in reads, and since YAPT does more of a command-line-level type of bulk write, it was able to more closely match its rated write speed when compared to how it fared in HDTach. This also coincidentally demonstrates how closely that limited write speed compares with the Intel 320 Series.