Don,
Is the lens you refer to the 50-200mm f2.8-3.5 ?
If so its probably not going to produce very good results
Point source light tends to bring out the worst in any optics, a zoom is likely to be worse than a fixed focal length lens and the 50-200mm being only an Olympus mid grade lens is likely to perform poorly for this sort of AP - it has a fair amount of chromatic aberration and lower contrast for normal photography and generally prefers to be stopped down 2-3 steps
So I think you would be better off using the ED80 - optically
But for focal length the 200mm would be better unguided as already stated.
You might like to read this article on dark noise on the E3 - its actually has quite a noisy sensor and longer exposures will make things worse.
http://www.wrotniak.net/photo/43/e3-dark.html
My early attempts using the E500 (different sensor) were marred by dark noise and sever amp glow that dark frame subtraction (in camera noise control) failed to control.
But getting started is the the first step - so see what it can do
Rally