For some of my fine art LF work, I'd like to print my drum-scanned or Hasselblad-Imacon Flextight-scanned 4x5 (100 ISO) negatives/transparencies to 6' x 8' in size.

That said, in your experience or opinion, how large can I print a single drum-scanned or Flextight-scanned 4x5 (100 ISO) negative/transparency before the resolution degrades into horrible/unusable territory?

I'm interested in the fact that Jeff Wall uses a 4x5 Linhof camera and is seemingly able to get amazingly high detailed and extremely LARGE (like 6' x 8') prints with just one 4x5 negative. How does he do that without the digital manipulation technique of combining many 4x5 negatives into a montage?

I'm looking forward to seeing what you guys have to say.