I think it depends on the cubes and power level.

I did the test years ago on a 557 with mildly ported 440-1's.
This motor was only making around 725hp.
I tested the 440-3, 440-3x, and 440-25 X-ram with in line 2 x 4bbl top.
On that motor the 440-25 was best, by about 20hp.

The -3 and -3x were nearly identical.

A few years ago we ran a 505 with some MM ported -1's on it, 750hp range, tried the -3 vs -3x and got the same results....... No real difference.

I'd say if you're at 540+ cubes and solidly into the mid-800hp range, that's when the 3x will start to show what it can do.

The only motors I've used them on had 572-13 heads, and both of those run pretty well, but I never ran any other intake on them.