9. ... f5 in the old/modern CK ain’t stupid

Caro, Tartakower, Kortschnoj, Donner amongst many others played Nf6 CK.

#30 #31
I stand corrected. Indeed Caro played 4...Nf6 e.g. against Berthold Lasker along 4...Bf5. Nimzovich invented the 5...gxf6.

Fun fact: gxf6 was supposed to be the better one of the two dubious ones (after exf6).

#33
Bronstein in "Zürich 1953" called 4...Nf6 superior to 4...Bf5. He mentioned 5...gxf6, but he did also play 5...exf6.
When Korchnoi played 4...Nf6 and 5...exf6 against Karpov it was commented as a provocation.

#35
You cannot pass a verdict on a single game. Otherwise here is a game with 4...Nd7
www.chessgames.com/perl/chessgame?gid=1070917

This was the latest corr. game that I could find. Black lost on time... Looks around equal though.