Inspired by the discussion with RU.08 I decided try to reduce the noise. It appears that due to the high resolution of the upscale, much of the noise inherent to the upscaling method can relatively easily be removed using an advanced filter, without a significant detail reduction. Here are some comparisons between the noisy and denoised SRV3:

Here are the comparisons with the Avisynth Spline64Resize:

http://screenshotcomparison.com/comparison/122116

http://screenshotcomparison.com/comparison/122117

http://screenshotcomparison.com/comparison/122118

The noise is now generally less than for the Avisynth Spline64Resize and less than for the source material.

Here's a denoised video sample:

https://drive.google.com/file/d/0B8_LYKyZDiajY1YwNGFHZmdEZUU/view?usp=sharing

The detail is retained, but the cost has been reduced. Thanks to RU.08 for keeping on the pressure. ;-)