Stats and figures are one thing but here are some quotes, thoughts and opinions we've been able to find from across the web regarding these switches.
On one hand, I’m very well impressed with the performance aspects of these switches and think that they are both excellent tactile switch options and competitive with current releases from other, various manufacturers and vendors on their performance metrics.
HPX is definitely a bit more assertive on the tactility than the original. I have the U4T as well, and side by side, they have a similarly sized tactility. The bump on the U4T feels a tad sharper, while the HPX is a tad rounder. Those are just my non-scientific comparisons.
The HPX has a large yet soft tactile bump. As a comparison, it is less aggressive than something like the Anubis.
In terms of sound, I found the handful I had to test to be more clacky (higher pitched) than thocky (deep), even when the stem rails were lightly lubed with 3204.
The HPXs could be used without lubing, but I recommend some 105 on the springs to remove the spring ping.