The horsepower increase that you got by removing the RamAir airbox filter is partially due to the increased airbox volume that's no longer being displaced by the filter.
To illustrate this effect, here's a graph that shows the effect of increased air box volume on a 996 using a EVR airbox. Note particularly the smoothing-out of the dip in the torque curve.
So if you're unable to use Pipercross filters in the air runners like RickyX, using BMC filters will probably result in the smallest volume reduction and least degradation to throttle response.
You can read the full explanation here:
http://ducatisportingclub.com/xmb/vi...=1701#pid12578