I don't really have 20+ mbit videos, but I have this

function SVP(clip Input) {
    SuperString = "{scale:{up:0,down:4},gpu:1,rc:false}"
    VectorsString = "{block:{w:8,overlap:2},main:{search:{distance:2,coarse:{satd:false,distance:2}},penalty:{lambda:20.0}},refine:[{thsad:100}]}"
    SmoothString= "{gpuid:11,rate:{num:2,den:1,abs:false},algo:23}"
    Super   = SVSuper(Input, SuperString)
    Vectors = SVAnalyse(Super, VectorsString)
    smooth_video = SVSmoothFps(Input, Super, Vectors, SmoothString, url="www.svp-team.com", mt=1)
    smooth_video
}

FrameRateConverter()

Please repeat tests with 1080p 20+ mbit bitrate AND 2x or 3x frame rate

BOTH modes are BAD, at least for this extremely low-quality source
this doesn't mean they're ALWAYS bad, I believe SubJunk made a lot of comparisons when he selected these values

set algo=21/23, mask.area <= 50 and you'll be fine

If you want to do a fair comparison that is simple to reproduce and analyse, write two plain scripts, w/o any "interframe" or "FrameRateConverter" in use:

1. MSuper(...)
MAnalyse(...)
MRecalculate(...)
MSmoothFps(...)

2. SVSuper(...)
SVAnalyse(...)
SVSmoothFps(...)

Besides what's exactly the purpose of using those 20-yo-320x240-clips in the year 2017? it looks like shit in both cases...

Observations:

- The difference between Interframe and FrameRateConverter is HUGE!

- SVP/Interframe always appears softer, as if it was applying some level of frame blending on every frame (I had this issue with scene change mask being 16 for black and 235 for white, which caused unwanted frame blending)

- On dreaded frame 4477, Interframe shows a "hard blending", followed by that same image mixed with ugly artifacts, which brings an original frame followed by gradually increasing artifacts on a still image.

Prefiltering only has a very minor effect. Variance without would be less than 0.01%

as I said before, may be (!) the major difference comes from

prefiltered = RemoveGrain(C, 22)

No, removing that only did an extremely minor difference.

What do you suggest?

prefiltered = RemoveGrain(C, 22)

nothing can stop you from pre-process video before svpflow

=======

prefiltered = RemoveGrain(input, 22)
super = SVSuper(prefilter,"{gpu:1}")
vectors = SVAnalyse(super, "{refine:[{thsad:100}]}", src=prefilter)
smooth = SVSmoothFps(input, super, vectors, "{rate:{num:2,den:1}, algo:21, mask:{area:50}}", mt=threads)

=======

 BlkSize    = Default(BlkSize, C.Width>1200||C.Height>900 ? 32 : C.Width>720||C.Height>480 ? 16 : 8)

you know you'll get significantly different results for the same video scaled to different sizes, right?

this's the idea
mask resulting frame with two source frames in "bad" areas, where "bad area" means "area with high SAD value of the motion vectors"

"external" implementation requires 10 lines of avisynth code and is slow as hell
"internal" implementation requires just another multiply-add operation for each frame pixel

Maybe add a new sub-menu in SVP Control Panel, under Artifact Masking, add "Enable Experimental Masking" with options (Enable/Disable). For us to test.

.. but as you say, finding it might not be so easy.