Tim-If my budget was twice what it is, I'd almost certainly be ordering a 2.5" loft Epiphany, but as it is, I'm fortunate enough to cohabitate with someone who studied textile construction in college and understands things like 'french curve' and 'differential cut.'
Brad-I had considered losing some of the width for the seams, but hadn't though about what I'd lose in loft. Hmmm. . . well, I have to make experiment with measurements, but I could probably make due with 52" shoulder width and use it as an under(rather than over)quilt with my 55"shoulder Arc Specialist. I fit okay under a 48" wide rectangular JRB quilt as a stomach/side sleeper, but some gaps do open up when I roll over. I think 4" of extra width(plus using the understraps, which I never do as its a 40 degree quilt and drafts aren't a big deal at those temps for me)would still be okay.
But assuming thru-hiker sells me genuinely 60" wide fabric, if I lose 1" for seams + 1.5-2" for 2.5" of loft, I should be okay at 57-58" of width. I'm probably going to go for your denser fill, as I believe Richard Nisley showed that there can be some benefit from that. The Nunatak Arc Alpinist has 11 oz of fill for 2.5" of loft, and so I figure 2.5 inches of loft with maybe 14 oz of fill will get me to 15-20 degrees.