The 'geared' belt driven idea sounds juicy. I thought you might get a few more replies on this, regarding how others do it successfully. There's not been any definitive answers yet, or at least a bigger sample of a variety of solutions that work for different people. It may be that there are so many parameters that need controlling or considering, and you just have the odd one not in your favour, but I hope you don't have to resort to too much empiricalism to sort it.