I think not, as video encodes require the CPU power to drive them,
you will be able to pull it off with a Quad Xeon machine, which will encode much faster then your Q6600, as i see on our clients machines, which encode videos, they like takeing the Quad Xeon or Dual Quad Xeon machines.
So a 2.4Ghz core 2 quad is capable of doing 3 encodes with out slowing down the site. How many could a 2.4Ghz Quad Xeon do. And also how many could 2 x 2.4Ghz Quad Xeons do without slowing down the site.
FFmpeg uses up to 100% of 1 core per process, doesn't matter the speed of the core. If you have a quad expect 3 conversions, if you have 8 cores expect 7 conversions max but you also have to consider RAM and disc speed.
An alternative approach is to using FFmpeg with multi-threading support, depending on codec support, which can potentially mean 1 video uses all 4 cores for instance. Sometimes this approach is faster than running multiple parallel encodes. I think a little bit of experimentation is in order