Bind mount point is 100% better then Storage backed mount point.
I run five parallel dd to both and speed is almost double in bind mount point
Used same old disk both both test, 7.2k disk.
dd if=/dev/zero of=test1 count=10000000 &
This is to storage backed mount point,
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 91.7577 s, 55.8 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 91.7576 s, 55.8 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 101.514 s, 50.4 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 102.352 s, 50.0 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 102.596 s, 49.9 MB/s
Same disk converted to local mount on host and then bind that to guest,
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 34.1297 s, 150 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 36.7766 s, 139 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 51.3204 s, 99.8 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 53.4467 s, 95.8 MB/s
5120000000 bytes (5.1 GB, 4.8 GiB) copied, 59.5659 s, 86.0 MB/s