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.
This application will be a 572 with 440-1 345CNC heads on alky making around 950ish hp. Just wondering if it is worth it to go to the "X" version of this intake before investing in the machine work for the injectors and port divider work.
