Guys: I can answer part of that since my engine was on the stand in August of last year. Single carb - 427 ci - side oiler.
w/ H&S air assembly 523 hp
w/ NO filter 543 hp
w? K&N Dual quad oval a/f 534 hp
The trq. was affected a little but I was quite surprised at how LITTLE the H&S filter robbed power!
At only a 4% loss it pays to filter and have the classic look. IMHO