Does the new process engine in C1 v7 have any superiority over up-sizing the image files than version 6? Are there benefits to doing step-wise increases in up-sizing? And lastly, is there an upper extreme of how much you can up-size before negative effects? Happy Holidays everybody, by the way...... Cheers!
Based on my analysis, there is nothing magical about the upsampling of Capture One Pro V7, just the convenience of not having to deal with it in another application. In fact, even (!) Photoshop CS6's BiCubic Smoother performs a little better in avoiding artifacts, and produces a slightly higher MTF (an MTF50 at almost 9% higher spatial frequency, at the 250% upsampling which I tested using the slanted edge method).
The exact effect on a real image of course depends on the image content as well. Capture One produces a bit more halo at sharp edges, which may look interesting on some subjects, but halos are artifacts I'd rather avoid in a generic procedure with no specific controls to mitigate the effect. The halos are not extreme, but I prefer to do my own output sharpening when the best results are required, and halos just get in the way of that.
For the best output I still prefer a dedicated upsampling application/plugin such as Photozoom Pro, which is a great companion for the Raw conversion quality of COv7.