Quick update. I've been looking into this further and have now found that xorg appears to be the CPU hog.

I've got the following errors in the Xorg.0.log but still not finding much to go on.
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I'm after some tips on where to start trying to find the cause of intermittent lag running BT5 R3 on a dell Latitude E6410. Its installed on the local HDD with a duel boot to windows 8, which is...