The verify read speed will depend on the optical disc drive and media type used in the writing session. For example, I found that with BD-RE media, all of which are limited to a maximum write speed of 2X, can verify throughout the entire disc space at a constant 2X only, even if the drive may normally read 2X or higher with BD-RE media. I've never fully understood the reason for the verify phase linear read speed across the entire disc, as it seems to be a separate read mode compared to the ODD's normal read mode under operating system access which would have varying speed depending on the read position on the disc. Perhaps L-UK might be able to shed some light on why this is the case (I noticed this with Pioneer BD writers and on multiple ODD writing software, including Imgburn). With BD-R write once media, the verify speed behaviour maybe different. It will also depend on whether the ODD will use CAV or CLV modes at the maximum read speed set for the ODD.
BD quad layer media is not currently available standalone, certainly not as far as I'm aware outside of Japan and I've not see it available for the Japan domestic market either. The only way to have access to BDXL-QL media is if you're going to buy an expensive Sony or Panasonic ODA Optical Disc Archival professional-use cartridge, disassemble it and use the BD media (taken out of the cartridge), which is only available as write once for quad layer 128 GB capacity. Most BDXL drives, though in theory should be compatible with BDXL-QL media, do not have internal media tables with any BDXL-QL media either, as far as I know. The realistic capacity supported at this point for BDXL-R and BDXL-RE is up to triple layer 100 GB discs, which have layers numbered layer 0 to layer 2. For a BD drive that reads in CAV constant angular velocity mode, the data transfer rate will rise from the start of layer 0, then peak between the crossover point of layers 0 and 1 after which it drops again to a minimum between the crossover point between layers 1 and 2, and peaks again at the end of layer 2 if a triple layer disc is used.
In practice, if you want the highest data integrity and defect management for BD-RE media, the realistic practical effective WRITE speed will be somewhere around 0.8X to 1.0X if you have selected 2X write speed and have enabled spare sectors on the disc during formatting of the disc beforehand.