Oh, jeez. X6 on hard? I had trouble on the easy setting... I feel X6 is the hardest in the X series.
Took me 2-3 hours just to get through on 1 stage, including boss battles (with High Max being the strongest outta them, in my opinion). Sigma here is, as reviewers say it, crazy, in a lame, de-buffed way. And I wish he wasn't, maybe he'd put off a better fight rather than his last form losing more than 3/4's worth of HP with the Shadow Armor's Giga Attack!!

And yeah. I will agree on X6 being the hardest. Trying it again on Normal, and this time, I set in the Nightshade Zero code before starting.
PS: The Ending theme was nice.