Every combination is different and you have to try what you have access to, or be willing to buy and experiment.
I have never tried a 1" spacer on a Victor intake. I gain on a Victor when going to a 2" spacer but I gain a greater % on a single plane M1 than I do on a Victor. I didn't gain enough to spend the money when I used a 2" spacer on the Super Victor for the 426 small block.
