576 frames of 4K uncompressed AVI would result in Gbs of data writing.
So this is not a "true" iClone render test.
Portion of the test is... just testing your system IO speed.
Copy resulted render file to the same drive and time it.
Then deduct that time divided by 2 (given read/write is at the same speed) from iClone render test.
That would give you a more or less true GPU render speed.

You can say I will render to MP4, it would be very small render output file and does not impact IO at all.
But here you have another burden - a compression which puts a toll on a render speed (one area which might need to be improved- only RL can tell).
And again amount of VRAM does not affect render speed. It is a speed of VRAM and GPU architecture plays a major role.

I got another one for you.
"New" users might not know and "Old" users sometimes forget...
But the screen resolution and view-port size would impact your render speed enormously and would influence the quality of the render in a way.

I got an old i7 2600K CPU, 32 GB of RAM and a pair 1080Ti (second is for Iray render only). All drives are SSD
And I ALWAYS render with Full Screen.

So those are my numbers for your project:
2K, 4K is render Frame Size
ON 2K, ON 4K, is my screen resolution
All renders with "Optimize with Full Screen Render" checked

2K ON 2K MP4 - 40 sec
2K ON 2K AVI - 43 sec
4K ON 2K MP4 - 129 sec
4K ON 2K AVI - 145 sec

2K ON 4K MP4 - 123 sec
2K ON 4K AVI - 127 sec
4K ON 4K MP4 - 92 sec
4K ON 4K AVI - 119 sec

Funny isn't that with full 4K screen 4K frame renders faster than 2K. Don's know if anyone gets the same but that's how it is on my system.

However the quality of 2K rendered on 4K is better than 2K on 2K.
Although on this particular project it is less noticeable than on some dynamic project with a lot of straight lines (like walls, buildings...) moving across the screen under certain angles.
Worse yet if you have some small GI emissive lights in various forms in a project and then they flicker like crazy on your render and you wonder why...
That is when you will learn to appreciate anti-aliasing (by enabling super-sampling, or rendering on hi-res screen and enabling "Optimize with Full Screen Render").

So the bottom line is, do not always chase for the fastest render time for every other project.
When I choose how to render and knowing about most of the quirks of RL render engine, I'd rather go for the slower, but quality render.