When Apple released 10.5.6 it contained a major bug which made tethering with USB cameras (e.g. Canon 1Ds III, Canon 5D II) unstable in any capture program. In Capture One this manifested itself as an application-freeze after about 110 raw frames, rendering 10.5.6 useless for those tethering USB cameras.. This bug *appears* to be fixed with 10.5.7. Our Head of Technical Services, Doug Peterson, has just fired off 500 shots on a Canon 5D mark II and is still going.
We will do complete testing, and post a side-by-side speed comparison soon which will include the incredibly fast P40+ digital back as soon as time allows.