Meh, I just went unarmored due to obsession with the Z-Buster. Quite a love-hate relationship, though, seeings how X5's was rather crappy.
Thing is, at least it's unique. 4th Armor does absolutely nothing that Ultimate doesn't. So, yeah...
The dash length in itself is not increased, but Speedster's overall increase in horizontal movement increases the distance that you cover.
So what you're actually gaining is jumping/falling distance? Well, that's not what I was talking about, but thank you.
Finally got un-lazy enough to test for myself, and yes, Hyper Dash does in fact slightly shorten your air-dash length. But it looks worse than it is, due to the sharp difference in movement speed; in truth PS1 air-dashing as a whole blows anyway (and yes the same all applies to X6's Falcon; I was wondering if it might be exempt due to appearing to be X5's flight in a fixed direction/length, but not so).
However, I did take notice, in the same manner that Hyper Dash
increases your dash length when combined with Zero's F-Splasher in X5, it does the same for Blade Armor's Mach Dash in X6. You can catch some serious air that way.
Oh yes, and I confirmed for myself that contrary to what many have said (this comes up in many an X6 discussion), Speedster does not enhance dash-jumping. As expected, if your dash speed is applied, it overrides Speedster; that's as true in the air as it is on the ground, with or without Hyper Dash.