Rich, my actually sentiment is you shouldnt go beyond 60" for 1920x1080 resolution, regardless of the screen technology. 1080 blown up to larger than 60" just looks too grainy to me at many avg. living room viewing distances. 10-15 feet. When 4k hits my price point in the 80" size screen, I'm in.
I'll respectfully disagree with you on that point, at least in regard to plasma. I've got 20/20 vision, and I have to stand closer than 8' to my 65" plasma before I start to discern any 1080p grid pattern.
Also, "graininess" may have to do with LED vs. plasma and personal taste for PQ. E.g., many LED displays still look "digital" to me, compared to plasma. That said, the PQ gap between the two technologies has significantly narrowed the past year or two, at least to my eyes.