If you google about a bit, there's a page I recall where someone has actually taken some astrophotos through a good APO (FSQ or TV NP) and a 20k Canon or Nikon 500mm pro lens. I seem to recall he favored the lens for sharpness, aberration control and colour. But after spending that kind of cash on a lens you'd provably be able to convince yourself it worked better than the VLT...
Cheers
Andrew.
found it !
http://www.samirkharusi.net/televue_canon.html