Tmpfs for mysql tmp dir questions
If your 50 connections all want to do SELECTs that need tmp tables, even small ones, they could overflow tmpfs and fail right and left.

I prefer to let tmp tables be in the same filesystem where everything else is.  That way, it is not arbitrarily causing trouble when there is a spike in traffic.

Meanwhile, I keep track of the slowlog and aggressively tackle any slow queries.  Note that queries using big tmp table tend to be slow, so the slowlog generally catches them.

Generally, optimizing a query will provide much more than a 50% improvement.

Optimizing queries decreases the "load".

50 concurrent connections actually active simultaneously running (not just "Sleep" in SHOW PROCESSLIST) is unacceptable in my book.

When a query dies, it should remove the tmp table.  If the server crashes, there is a chance that the tmp table will remain.  This often happens with ALTER.

When a write operation dies in the middle, and the table is Engine=MyISAM, the write will be partially finished, and there is no way to know how much was done or not done.  Examples:  INSERT ... SELECT ... and DELETE ... WHERE ... SELECT ...