1) "libsofia only handles 1 thread per profile, so if that is your bottle neck use more profiles"
Is this still true?

This is still true.

3) "On a normal configuration, core.db is written to disk almost every second, generating hundreds of block-writes per second. To avoid this problem, turn /usr/local/freeswitch/db into an in-memory filesystem."
It seems the other alternative is:
"-nosql -- disable internal sql scoreboard"

What does -nosql disable? e.g. for a dialer trunk you don't need presence, track-calls.. can you still get an active call count from FS?

You'll also lose commands like 'show calls' and 'show channels'. Possibly some registration information too, since that's stored in the core DB too. I forget whether -nosql disables just the core DB or the sofia DB etc too (I never use it).

As well as using a ramdisk, using ODBC can help too - the proper databases are far better geared to scaling/concurrency than SQLite which is more for small-scale/embedded systems. It can also offload the database load onto an entirely separate server.