If you buy a dedicated flash for your 40D you won't benefit from the 'dedication' whilst using it with the Yongnuo remote triggers. They only fire flashes manually, they don't pass on any TTL / exposure information. So your dedicated flash, when used off camera with these triggers, will work the same as the flash you have now.
To use the TTL stuff off camera you would need triggers that can pass that information to the flash (without checking it out I'm not even sure there are any) or you have to have a physical connection between the camera and the flash, i.e. - a sync cable.
I'd personally recommend learning to use flash in manual mode as it will serve you better. The TTL stuff is okay but it's not perfect. You only have to learn manual flash once and you can light anyway you want with consistency from shot to shot, which you won't get with TTL.
I think the 40D sync speed is 1/250, so setting it at 1/200 will be fine. That doesn't mean you'll get a good exposure, correct exposure of the flash light depends on the power of the flash, distance of the flash from the subject and the aperture used.
Try your light in fairly close and use a middle-ish power, like 1/4 power, and set your aperture to a large-ish aperture, like f/4 or somewhere. Take a shot.
If it's not bright enough then you can either choose a larger aperture (if you can go larger), move the light closer which will also make the light falling on the subject softer, turn the power up on the light, add another light and if it's still not bright enough there's always the ISO that can be raised.
If it's too bright then you can either choose a smaller aperture, move the light further away but that will also make the light falling on the subject harder, turn the power down on the light or go to a lower ISO (if your not at your lowest already).
Just adjust to taste. It's quicker with a flash meter, one pop and it tells you what aperture you need for correct exposure on your subject from that light.
