I would be interested to hear what you consider high volume (writes/second). I am supporting a manufacturing system and it sits at the moment at 7 000 writes/second (it is a normal time series, ie id,time,value,quality).
Though it's not usually write throughput that most of these technologies are worried about. It's usually compression using dsp methods, aggregate stream folding computations, etc... that matters.
From an IoT or sensor network standpoint, 7000 writes/second is an idle server.
If you want a database for blazing fast data-storage and retrieval, there are many options available. You start seeing the real benefits of kdb+/q when you use q to simplify very complex operations that aren't easily done in SQL. Also, the high level operators that q makes your code extremely terse. I've written complex backtesting systems that perform data mining on massive datasets - all in one page of very tight q code!