I have to agree, I have some fantastic 12"x16" prints on my kitchen wall made from 35mm Velvia 50 transparencies. They really are extraordinary considering the degree of enlargement. If they were there on their own, I would be delighted with the quality. The problem is they're next to 12"x16" prints made from 6x7 velvia transparencies. If you're about eight feet away, the difference is marginal, at four feet the difference is obvious and at two feet you start to wonder how a little rectangle of film can hold that much information. Don't get me started on 4x5 guys, I can't afford it!
I have some prints - Cibachromes - made from 6x7 Kodachromes. I wish I'd made more when the Ciba stuff was available.