WH16NS60 vs. WH16NS40, yes it's 8.0X max vs. 6.0X max, what will the average speed be well your results will vary and depend on a number of factors. The NS 60 is not consistently 25% faster in real life and posting results of one off tests should make it clear that no one is guaranteed those speeds. You try and run a dirty scratched disc you got out of RedBox through your drive it may or may not make it compared to brand new fresh out of the package disc. Important part is to always clean each disc with LCD screen cleaner and microfiber cloth before ripping, give it a fighting chance.
Speeds for UHD Blu Ray rips wil differ from those of standard blu ray rips and DVDs. Why? I'm not sure but I very rarely see a blu ray ripping at the same high speed as a UHD blu ray.
The most useful speed information in my opinion is which drives have top read speed of 8x (ASUS BW-16D1HT, LG WH16NS60).
and those whose max read speed is 6X (everything else unless it's cross flashed: LG slim drives BU40, BU50, WP50NB40, BP60NB10, LG WH16NS40, 14Ns40, 12NU40, ASUS BC-12B1ST, BW-12B1ST, BC-12D1HT. There are more, and your results may vary that's what you need to remember.
What's important to know is a drive that maxes out 8X will not reach 8X and stay there. The ASUS 16X and LG NS60 if you watch may hit 8.0X or even 8.1X and then settle back down to a speed they can keep consistent without errors. Generally this is between 6.8 and 7.4X, and you will only see these speeds when the rip cycle hits the main .m2ts file, the meat of the disc, the ginormous file that's 30, 40, 50GB. Gives the drive time to stretch it's legs and open up.
LG slim drives BU40, BU50 they will consistently hit max speed of 6.0X and stay pegged there for awhile. Take the throttle off they could probably go a lot faster, which would result in them rattling themselves apart prematurely.
In my experience when you cross flash the 8X firmware to a 6X drive you'll get almost speeds as the native fast drives, f course there are other risks with cross flashing that have been discussed.
So if you're really interested in speed, sit there and watch a rip, you'll know when transitions between layers are reached and when new files start as you'll see the speed change, often back to 0 and then the slow ramp upwards. Then deep into a rip when it's in the high 7s and slowly ticking up to 8X, is it going to get there? You watch and watch and then it hits 8.0X and then you're on the bow of the Titanic yelling "I'm the king of the world"! And then it's all downhill from there, much like the Titanic