I haven't used vacuum advance on any of my hot street cars in years, I did hooked up the vacuum advance on my 1969Dart GTS 383 4 speed to the stock location for ported vacuum, I didn't see any gains or losses with that car
I do set all my distributors up to have between 14 to 18 degrees at idle and no more than 34 degrees total So maybe that has a lot to do with my results