Input delays in Aces High have nothing to do with the Internet connection, unless your connection is being spammed from the outside, or you are running downloads from the Internet.
Basically, any input delay is directly related to the computers CPU and how busy it is. If the computer is running out of any resource (system RAM, video RAM, sound channels...), it can cause it. If there is a high CPU usage outside the game, it will cause it.
Start with a DXDIAG output and let's see what resources are available and then we can make suggestions on what the game settings should be like. While we are at that, take a look at the CPU activity with nothing running on the computer. Using the "Windows Task Manager" take a look at the CPU usage in the "Processes" tab (lower left corner). It should almost always be at zero.