Check the "use VDP1/2 Draw/CD Block thread" options. The checked part will then run in a different thread, so in theory SSF supports up to a quad cpu system.
You can also set the Slave CPU to 100% speed and the dot clock to higher for better compatibility, of course that will have a significant performance hit. Thats why a multicore CPU comes extremely handy.
No, unless you mean two 2400mhz cores in one cpu. The actual CPUs runs at 2,4ghz which would roughly equal a 3800+ rating for a single core Athlon 64.