The difference being of course that I've statted mostly small to medium-sized creations
The main reason I use fixed armour values is because I only have d6s and exploding dice could mean a guy with an SMG could take out a small tank in one shot if rolls got really weird. I'm also not a huge fan of combined small arms' fire taking out a vehicle, but the 'armoured' rule can cover that. If units with heavy weapons can still combine fire the armoured rule also isn't too powerful imo, whereas otherwise it kinda is. It also makes the game a bit more tactical because it makes your heavy weapons guys more unique and important. In a few games I've given their weapons 5 UR to make them less effective against other infantry and still allow them to hit vehicles most of the time and beat their armour, though they'd still have to combine on bigger creations.
So a not-too-high fixed armour value and 'armoured' is the way to go imo. After all there's also always the aiming bonus, component damage, grinding... that help beat creations down. Though I feel not a lot of people seem to use this.
Actually finding the right armour value for balancing things out can be tricky though and I'm still looking for it on many of my creations. I recommend play-testing before taking it into battle
If you wanna kill something as big and awesome as this tank though, I recommend you'd better build something to match it, because we all know that awesome > purely practical.