Transitions and message "GPU memory full"

Since today I am also a proud user of the studio version, which uses my NVIDIA GTX1660 very well and is therefore more powerful when rendering than with the free version.

But - If I want to create a transition between the 4k50FPS clip and the 4k30FPS (no sound) clip, I have to use 2 tracks. For example, if I cut the 4k30 clip and create a transition in between, I can do that in the same track. Is that related to the different clips (FPS) or because of sound / no sound?
And then I cut the 4k30FPS clip 2x (thus created 3 clips) and edited each clip with color grading and noise reduction - then the message comes that the GPU memory is full and I should either reduce the resolution or the corrections.
Is there another option? And - how much graphics memory should the graphics card have in order not to receive such messages (currently I have 6GB)?

Minimum of 8Gb, probably more....because you're using (multiple) 4K media. The error is very common on Nvidia GPUs.

It's probably the NR causing the problem.
You may be unable to export 4k with NR and only 6GB VRAM.
2 workarounds you might try -
1) Export with everything except NR at high bitrate. Re-import, add NR then export final.
2) Export everything at 1080p at high bitrate. Re-import and supersample 2x for 4k export.

Thank you for your answers!
I only got the message after using the noise reduction video filter.
What do you mean with NR?

NR=noise reduction

OK - thank you Now it is all clear.