Is there some overhead to Write speeds of an SD Card?

I just bought an EOS R, and when recording 4k in all-i mode (8-bit LOG), it usually shuts down after 30 seconds or so (giving me an error, shaming me over my slow sd card).

I know, though, that it records at 480 mb/s or 60MB/s, and my card goes "up to" 150 MB/s. After testing, I can see the the WRITE speeds of the card are consistently bove 75MB/s (around 80 usually).

That’s why the question: is there some overhead to the 60MB? Am I too close to the limit for the camera to function normally? Will I be safe if I can get a card with write speeds closer to the limit of 100MB/s of UHS-i? Or will I have to get a UHS-ii card?