Hate to think how much that would cost.I hear you.
Speaking of prized lenses. I saw a 50mm f/1.0 L in a shop a while back. I still drool just thinking about it. The price tag was a bit out of my range though.
I've never regretted not getting the f/2.8 or the f/2.8 IS. The f/4 is plenty good enough for my needs.