Unless your database server has multiple processors it is unlikely that running multiple
queries in parallel will be substantially faster than running the same queries serially.
Not necessarily true. Compiling a large project (say, a
linux kernel) on a single CPU machine completes substantially
faster with two processes (make -j2 ...) than
it does in a single process, as this allows the CPU to keep
compiling in one process while the other waits for disk
access.
While I haven't tested whether this is also true of databases,
I suspect that it is likely to be.