It seems as if someone did some testing and found out that the max belt speed in 1.1 is 360/s, not the 270/s that 0.17 is limited to. https://imgur.com/SjFcZai for proof. Given the tiers in this mod, that would mean two extra tiers, one at 315/s and the last tier being 360/s.

those counters are unreliable.

They are unreliable. Y'know why? Because the maximum is actually higher than that. https://imgur.com/a/b67NaHi for proof.
I did some testing as well, to confirm 360/s, but actually confirmed 480/s.

that figure is also wrong.

the only accurate count will be gained from the production flow API (production graph window)

You are right, the cap is indeed higher than 270/s, at least when I last tested (using the production graph). I cannot speak of the accuracy of those counters, but I don't doubt you can have belts faster than 270/s. I think even faster belts than I've currently added would be cool, but I'd have a hard time figuring out how to cost/balance them and evaluate their usefulness. The reason is my computer can't even keep up with a megabase that can make use of current top tier ultimate belts.

Secondly I don't really have the time to do it currently :( I have other mod ideas unrelated to belts that would be cool to create too, but I don't have the time right now. I love your interest in my mod though :)

i have the Express Bus mod that is useful for aggregate busing.