unittest_main has verbose flag to control log level: https://github.com/mongodb/mongo/blob/master/src/mongo/unittest/unittest_main.cpp#L122
It would be great to have the same for benchmarks: https://github.com/mongodb/mongo/blob/master/src/mongo/unittest/benchmark_main.cpp#L43

It can be useful to be able to change log level without re-compiling code when adding or debugging benchmarks.