I have added some more information on the comparsion, have a look at my updated
200 Comparision. There is no question the in my mind the zoom is sharper, but bright stars are "less pleasing" and there is more vignetting when compared to the prime. I suspect the prime is more contrasty, but haven't actually verified this. But the zoom gives you a very nice 70 f2.8, 100 f2.8 and 135 f2.8 included in the price and it is also extremely well made.
Keep in mind this zoom was hand picked at local camera store so it shows almost no decentering (as is a common problem - actually the norm - with camera lenses). Decentering is the problem where misalignment in the optical elements causes one side of the image to come to focus before the other and can cause other problems with Image quality.
Terry