In my experience, there is a difference between premium SKF bearings and Chinese copies, primarily in durability and resistance to external factors. The rolling resistance is so low that I didn't notice the difference. My driving style is far from consistent and I am far from being able to notice such small fluctuations :)
I found information on several forums that premium bearings at the beginning of use, the first hundred kilometers or so, have a little more resistance - probably until the lubricant is brought to working conditions.
What I noticed during maintenance is that the durability of premium bearings to lateral forces and the sealing of the cartridge is much better. I noticed this first of all on the bearings of the main pivot of the suspension, which are the most exposed to such forces and dirt. It is very difficult to notice differences in durability on hubs since any bearings literally last for tens of thousands of kilometers without problems, as you yourself noted. What I was guided by when choosing premium bearings is the fact that the process of replacing bearings in a free hub requires a lot of work, so even the potential delay of service for several months or year is reason enough for the investment.
Gotcha! I might try SKF on my GXP cranks. GXP are notoriouly faulty in terms of design, but perhaps better bearings will help... Enduro (brand) bearings didn't last, not to mention cheap ones.
Yup, it's quite annoying. I do have the tools, however. Bearing pullers, press and all that stuff you can find fantastic quality ones on Aliexpress
I have no experience with the Sram GXP set as all my bikes use some Shimano hollowtech. Wheel sets are DT Swiss & Shimano XT, so no Sram there neither :) Anyway, I hope good bearings will help. Let me know how it went when you have some conclusions