if the Xenomorphs ever became that size, I'm fairly certain the universe would be unable to stop them. Not without copious amounts of nuclear weapons. Or the wormhole weapon from Farscape, that may be able to do it.
Those are some might big aliens! Must have impregnated some dinosaurs! Fantastic detail in the piece and I love the sort of misty background look. That predator has his work cut out for him. I'm a bit biased though, so I think I'll be routing for the aliens!
This indeed should be a fight to test his strength. The guy has the will and strength for it. But this will prove his abilities. Also, the art work, Its detailed, amazing. Love it. Extremely impressed with the curving you added into both creatures.