The lag is caused by your client waiting on the server to make the change and replicate that to you.
You have to apply the speed change to the client and then call the server to make the change.
DO NOT MULTICAST CMC Movement Changes.
Input → Can I change Speed! [TRUE] → Change speed on client → RPC Server
Server → Can I change Speed [TRUE] → Change speed on server
This is the simplest it gets.
