For real workloads it is complicated and for now I include benchmarks in "real workloads". Here is one interesting result from my IO-bound tests of Linkbench. The summary is that when you spend less on IO to write back changes then you can spend more on IO to handle user queries. That benefit is more apparent on slower storage (disk array) than on faster storage (MLC NAND flash) because slower storage is more likely to be the bottleneck.
IO-bound Linkbench means that I used a server with 50G of RAM and ran Linkbench with maxid1=1B (1B nodes). The MyRocks database was ~400G and the InnoDB database was ~1.6T. Both MyRocks and InnoDB used MySQL 5.6.26. The workload is IO-heavy and the database working set is not cached.
The interesting result is that the difference between MyRocks and InnoDB becomes larger as storage gets slower. Another way to describe this is that InnoDB loses more performance than MyRocks when moving from faster to slower storage. I assume this is because MyRocks uses less IO capacity for writing back database changes so it has more IO capacity for handling user queries.
Transactions per second
MyRocks InnoDB MyRocks/InnoDB
Disk array 2195 414 5.3
Slow SSD 23484 10143 2.3
Fast SSD 28965 21414 1.4
The random operations per second provided by the storage devices above is approximately 1k for the disk array, 10k for the slow SSD and more than 100k for the fast SSD.