Uhm, no. The Mark 5 was when the Red and Gold suit was streamlined even more, microcircuits vs printed circuits were installed, rivets were removed from the face plate of the helmet and hip pods became a power supply for him.
The Space Armor is considered among the specialty armors, like the sub sea armor and the Stealth armors.
Mark 6 would be the Silver Centurion armor that debuted in ish 200.
You might be right, I just always considered the specialty armors as marks because the were new armors and upgrades