Yes, I remember MultiCX. I was a big fan of it back in my WB 3.1 days. It took care of many things for one commodity. I abandoned it when I went to OS 3.9 though. I do not recall the details but it was conflicting with something or just caused the system to freeze. I believe I learned much later that something else was to blame. This discovery was made in emulation because my A3K was sold off by then.
I am using OS 3.9 again with an A1200 and was able to install the OS 3.x compatible MultiCX but I also remember now about shareware reminder nag window and the author being unreachable to do anything about it. It also is somewhat outdated with regard to OS 3.9 because it does not recognize the OS version correctly.
On the positive side, it does offer some more customization when it comes to mouse acceleration. I will have to play with it some more.
I did locate an MCX v2 key but it does not seem to eliminate the nag screen for the OS 3 version. I could also not be placing the key in the right location. Could not locate any instructions on this.
You can use various commodities to speed it up, slow it down, etc. I don't recall the names of any specifically but I *think* Multi_CX has this function. Plus many more. Check Aminet. 