Patrice:
And my other question is, does tor recognize this option?
MaxMemInQueues 7000 MByte
It does, see the man page or the source code.
Because I see nothing in the logs. I am not 100% sure but I think tor gave a feedback when I used this option in the earlier versions.
You will not see anything in logs until this value isn't good and was adjusted by tor. For details, see compute_real_max_mem_in_queues() function in /src/or/config.c.
-- Ivan Markin