Still working through fountain pens trying to find the finest of the extra fine w/o custom grinding. I think I've reached a satisfactory conclusion for now.
Platinum Century 3776 UEF wins by a (very thin and costly) hair but the Kakuno EF is not that far behind. The Jinhao EF#08 is decent but a tad thicker. All of them are better than the Platinum EF02 which is significantly thicker.
tl;dr: 3776UEF is best but expensive, Kakuno EF has best price/perf @ ~1/20th the cost.

All that said, no regrets here. The Platinum Century 3776 is a beautiful pen and the UEF nib is great.

A couple more inexpensive pens arrived and they are surprisingly good so far, so I added them into the mix.
- Jinhao 80 with "Iridium Ultra Fine" nib marked with "03", $10
- Asvine Forest(?) EF, $17 (Mine is "Matte Black Forest [...] by Asvine")
The 3776 UEF is still the winner but the new ones give the Kakuno ($13) a run for its money both in width and in price/performance.

The new arrivals look really nice, especially for being low-cost as these things tend to go.
I like the look/feel of this Jinhao 80 much more than the Jinhao 9019. The 80 is a Lamy 2000 clone but I don't have a real Lamy to compare.
The Asvine/Hongdian is all metal and has nice a weight, but not overly so. It's entirely matte black, including the nib, which is fun as well. Not everything has to be shiny and silver/gold!
The Kakuno's smiley nib is still the best, though.

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