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if you are using newbb2 then updating to CBB is painless.. as no scripts need to be run, all you have to do is copy the files to the server and then update the module in XOOPS admin to redo the templates..
then set the preferences in admin.. (also add a couple of css classes to your theme style.css file) all in all it should only take a few minutes..
to speed newbb2 up, i can't suggest anything brash hasn't other than turning off any features that aren't needed or used..