6600 was the last year before Shimano started futzing with cable pull.
From what I can tell Sram has never actually changed anything about cable pull on their road shifters and apparently just copied the early 10s Shimano blueprint for front shifting design (poorly).
7700 works too but they are harder to find NOS and the finish sucks/breaks down.
Haven’t looked lately but 6600 braze on pushers were dirt cheap for a while on eBay so I stocked up years ago when Sram front derailleurs were especially abysmal.
Can (probably) confirm. Pretty sure I have a 6600 gen Ultegra pusher on my Telekom gettin pulled by old SRAM Red.
It works.
I don’t even know where it came from, but when I got my mostly Red group from another Tarcker it came with a clamp style pusher and I needed a bolt style and it was in my parts bin…
I haven’t ever had a problem with my force 11 speed front shifting. I don’t remember having a problem with 10 speed wither.
my older 10 speed dura ace (integrated cable) was needy as fuck though as far as adjustments.