Thanks Alban!
That makes a lot of sense and good to know that the USB 3 connection has sufficient bandwidth to cope with my monitor at 60Hz.
I think I may have found a dock which meets my requirements from i-tec (
https://i-tec.cz/en/produkt/cadual4kdockpd-2/) which has 85W PD as well which will be useful for my MacBookPro 15" and appears to have the DL-6950 chipset.
Is there a reason why the i-tec docks aren't listed on the DisplayLink website? Are they not official partners or is there another reason? (Just checking whether I should avoid this dock for any reason!)
Cheers,
James