I've noticed you have to run a standard engine with the Cen, if you do that and try to have good weapons in the CT, you can soak up quite a bit of damage. I've seen them in the 10-20% armor range. Of course, that is not a very large load-out, but still respectable for it's endurance.
The heaviest I can comfortably go is with a Hunchback, with either Gauss or AC20. Though, I do think they need to fix the size of the Centurion. It's as large as an Atlas, which is twice its weight. If they fixed that, along with the width, it would be a pretty powerful mech.