"Kills" may be a bit enthusiastic, given Anand's comments...kills?
the 510 is faster in all but a couple of the real world benchmarks, but the difference between it and the C300 in every test is small enough that neither "sucks" or "kills" the other.
"Random write performance is also pretty low by today's standards, however the impact on most of our real world performance tests is minimal. It looks like we may have hit the upper limit of what we need from 4KB random write performance (at least given current workloads)."