Thanks for the reply zoombapup.
So you think I should make the local client authoritative over it’s position and on the server make a reasonable assumption whether a move is possible?
I’ve been doing something like this by sending the local clients position to the server via reliable RPC every frame just to keep the project moving in the meantime but I figured this would get bandwidth expensive quite fast with many players.
I think you’re correct, there’s no way to predict input in movement like this. I’ll try the client authoritative thing and see how I can optimize the data I’m sending and smooth some bits out with simple prediction.
I’ll check back in with my results.
On a sidenote when you said “our games” i did a quick google of your name. You worked on Worms! I guess its pretty clear where my inspiration i coming from then. 
I’m still missing the old days of roping in WA.
Thanks again!