Doesn't matter what board you use, 3.7GHz is a pretty good clock for a Q6600 and speed wise, for 24/7 use, not much will better it. If you only need dual core, you could try an E8600 at say 4GHz or above and that would speed things up a bit, but for number crunching/encoding etc, the quad will win.
I would wait and see what Nehalem brings, less than 3 weeks to wait and I think you will start to see some results being published next weekend/early next week.
If you can wait and are ok with spending the money needed to move to nehalem then i would say wait too.
If you dont want to replace the core components and have a £350+ish to spare then a Q9650 (E0) is a nice option and many will do 4/4.2Ghz.
However i dont think there will be £350 worth of perfomance increase.
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