Two that I have might qualify, not as "ultimate" but at least very collectable;
1: .45 cal, 16" "Buntline" with skeleton shoulder stock and scabbard - less than 35 were made.
2: 1851 Navy with .38 cal. Richards Mason cartridge conversion - again, less than 35 were made.
Not sure, but I think that only two of those "Sears" guns were ever produced. One was a pretty close copy of the original in .45 with mother of pearl grips, the other was .38 with bark ivory grips.
For me, the ultimate would be that original .45 Sears gun, even though it was made up back when they were using Uberti parts.