Hi,
a little test I made since I own both grabbers and 2 diffrent converters.
Maybe it could help someone.
Reference Screenshot
Taken directly from Windows desktop and scaled down to 720*576 PAL resolution. So the best you could get, in theory.
Fushicai UTV007 Grabber
You may notice massive sharpening. Makes outlines and silhouettes much brighter. Once Hyperion reduces the image for calculating the ambilight, it could easy result in wrong colors. Also a bit to bright so we lose information here (easy to see at the color bars on the bottom and greyscaled ones at the top)
However this is not only a grabber problem but a grabber+converter problem.
The screenshots I took with the other converter dont have these extreme sharpening problems.
STK1160 Grabber
Much better already I think. Less sharp, yes, but we need decent colors, not to much of details. Skin tones are pretty natural. Also the color bars on the right are not turned into "neon" like colors.
========================================================================================
I also tested CVBS vs. S-Video. But I had to lower my resolution to 1080p since my 4K Converter has no S-Video plug. If anyone knows a converter which supports 4k and S-Video please let me know!
So the following screenshots are in 1080p with the 1080p converter!
Fushicai UTV007 Grabber ( CVBS )
No overdone sharpening effect this time. Brightness seems to be fine aswell. Guess not every grabber works the same with every converter...
Fushicai UTV007 Grabber ( S-Video )
Not really a big diffrence huh ? CVBS seems even a little better (less interferences)
STK1160 Grabber ( CVBS )
Again the STK1160 delievers the better and more natural colors.
STK1160 Grabber ( S-Video )
This seem to be the best you can get. Less interferences compared to CVBS and even a little more detail. Colors seem to be the same though.
thanks for the test! all screenshots are taken with hyperion right? could you do me a favor and try to make screenshots with mplayer on the rpi? 
