Thanks for the idea, but those are no longer manufactured, and a 52T chainring + 18T cog only gives 4.7m development on the top speed, which is way too low, as I use this bike for touring — I know it's not its nature, but it rides well enough and it's more convenient to combine with trains/buses.

Too bad Sturmey-Archer' X-RF8(W) is heavy, noisy, and a bit unreliable; Otherwise, it'd be an easy solution to the problem.