Solved! Will a Samsung Note 8 take advantage of the speed of micro SDXC UHS-II V90 U3 memory card?

[johnm719]

Will internal write/read go at 250/300 MB/sec? Will transfer using USB port go at 250/300 MB/sec? Will any android phone do either of these?

 

[helpstar]

USB 3.1 Gen. 1 is specified so theoretically it can transfer up to 5Gbit/s if the device you connect it to will provide USB3.1 gen 1 as well

internal write speed should be limited by the sd card and not the phone nowadays, but check some reviews.

Samsung Galaxy Note 8 SMB, USB 3.1 file transfer speeds – Photochirp

 

[KnightShadey]

Will internal write/read go at 250/300 MB/sec? Will transfer using USB port go at 250/300 MB/sec? Will any android phone do either of these?

NO. It's capped at UHS-I

And despite Helpstar's comments, his own link shows this when the author is transferring from the SD card he is only getting 70MB/s, which is still pretty good for UHS-1.

Unfortunately the Note 8 (and Note 9) are limited to UHS-1 and 104MB/s speeds (minus overhead).
All Snapdragon 835 & 845 devices are limited to the "SD 3.0" spec (technically SDXC 3.01) which only includes support up to UHS-I.

The SD 855 introduced support for UHS-II found in the Note 10, but still crippled by Samsung.

Internal storage supports UFS 2.1 which caps out at 1200MB/s which is where you'll see it flex in Helpstar's link via the external SANDISK SSD.
I have a Samsung T5 (now also a T7) for external transfer (handiest for backups and 4K video transfers, and I could never get more than 83MB/s on an SD to SSD transfer on my Note 9 (with a 256GB Sandisk Extreme Pro [I didn't have bigger/faster cards until the N10+ ]).

Unfortunately the Note 8/9 also doesn't support low-latency App usages with A2 either (and Samsung crippled what A1 support there is), so a regular UHS-I / U3 / V30 / A1 is pretty much the cap for SD cards. (theoretically UHS-I V90 but not really)

https://www.qualcomm.com/products/snapdragon-835-mobile-platform

https://www.qualcomm.com/media/documents/files/snapdragon-835-mobile-platform-product-brief.pdf

(note the SD Storage / Memory sections in the Qualcomm 835 product pages)