Allow me to confirm what Mark just posted.
The Radiance scaling is designed for accuracy and not for additional sharpness. This is unlike what most other scaling algorithms appear to be doing. The Radiance default is no enhancements -- with the one exception that Darbee DVP(TM) is set to HD 40 by default per our agreement with Darbee. I can also confirm that there was a bug that would soften the image in earlier releases of the Radiance 20XX scaling that has been fixed in current release. So any comparisons need to done with current software.
The Radiance has 6 different edge enhancement controls. If sharpness is what you crave these can get you all the sharpness you could want. Just note that whether built in to a scaler, or independent logic, any sharpening algorithm - including what is in the Radiance - must by its very nature add artifacts. After all it is changing the image which is technically an artifact, although one that people seem to like. This applies to the Radiance edge sharpening, or Darbee DVP(TM), or any sharpness filter.
I would also like to point out that scaling is a small portion of the advantage of owning a Radiance. From providing reference level color calibration with the 729 point linear-Gamma CMS and 21-point parametric grayscale, to 2D/3D, and now for 4k (output), anamorphic control and adjustments, to blanking, sizing, position, etc., to per input resolution controls such as the Darbee DVP(TM) setting, to splitting off audio for 3D source to a 2D receiver, to any number of other setup and adjustment controls, the Radiance is the best way, and in some cases the only way, to achieve an optimal theater setup.