Picking flats is like picking an amp! so many options, vintage, modern, smooth, rough, high tension, low tension...
I have tried many and still have a set of Roto 77 waiting for a turn.
-Cobalt flats on my Peavey Foundation. Very bright when new, nearly round wound, as I'm sure you experienced. Took them something like 30 hours of play to mellow out and start really sounding flat. I do like these, though. They are now starting to show wear and tear after nearly 9 years of play.
-Chromes on the passive Precision and Carvin BB75 fretless. Not as bright as the Cobalts, but smoother feeling. These break in much faster the Cobalts and get thumpy, but are still not super vintage-y and retain some top end. Smooth feel. The catch is that I like 45 65 85 105 with these, and have to buy two sets to make this hybrid gauge. These are what I had on my Stingray, too, which sounded great. I like them thumpy, but still have that Stingray punchy bite. I'm sure the Kiloton would be similar.
-Fender flats on my active P. These are old, pre D'dro ones, like from 15+ years ago. Not smooth feeling, but do have a nice thump to them. They offset the extra zing of the electronics.
-LaBella Deep Talkin' flats on my Danelectro Longhorn. These are
very vintage sounding and
very smooth. Probably not what you are looking for. However, I'll get these for the Foundation when the strings have to be changed. I like how they break in fast and thump.