Expected performance hit? is it worth it with such low end hardware anyways?

Laptop: t14 gen 1 (thunderbolt 4).

Gpu: rx580 8gb (pcie 3 x16).

Dock: TBD.

Usecase: External monitor connected to egpu, casual gaming (cs2, deadlock) and video encode/decode.

From what i could find there is no real difference between tb3 and tb4 regarding an egpu aside from the fact that the controller is integrated in to the cpu instead of being an external chip (and tb4 being 32gbps guaranteed while tb3 allowed manufacturers to only implement 2 lanes if desired so you *could* get only 16gbps depending on the laptop).

My main concern is limiting the gpu to only 4 lanes, it's already a mid tier gpu from ~8 years ago, from what i could find the performance hit is anywhere from 10-20% which im ok with, still miles better than the igpu of the laptop, i'm just worried i'm missing something obvious and it will be way worse, also looking for recommendations on docks, should i look for something tb4 or just stick to tb3? as they should be the same on the dock side (well tb4 allows daisy chaning some devices but i don't really care about that).

I have a full size power supply and i'd prefer to use it, budget is tight if you couldn't tell already lol. I don't really mind if the dock is literally just a pcb as long as it works, i can get something 3d printed.