The longer the lens the more prominent camera shake is. So there is no set speed. Even with a monopod firmly on the ground, you still have 2 axis on which the camera will have movement potential. I have never really used a monopod for shake reduction, mostly for weight reduction (hold the camera and lens up for me). Maybe since you have steady hands, you can get a stop lower on the shutter than if you hand hold normally. But again it deppends on focal length.
If you don't know this. Basically most people can get steady shots by using a shutter speed that matches their focal length. In other words if you have your lens at 70mm. You can probably get a nice sharp focused picture at a shutter of 1/60. If you have a 200mm you should be at 1/200 (if your camera allows the selection of 1/2 and or 1/3 stops). If you can only select full stops then the choice would be 1/250 as the next nearest would be 1/125 and that may be too slow. For a 30mm again 1/30 should be good. Now some people are really good and can hold a camera steady. So, going by your own knowledge you know your 1 stop better than the focal length. So, now your 30mm limit is 1/15, 70mm now 1/30, etc...
If you add a monopod to the mix, you can possibly go a further stop slower than your known steady hand speed. Best way to find out is to do some test shots. Throw them up on the computer, and zoom in and check the focus. Longer focal length are more prone to show signs of camera shake. So, at the lower lengths you may be 2-3 stops better but that may deterioate as you go to longer focal lengths to where you are even or actually need to add a stop extra. Best thing to do is get a little practice in and see how you are.