I am currently playing a house rules campaign (Total war for Independence) and acting chivalrously has gained my reputation all the way to very reliable and given me chivalrous generals all over the place busting my cities up to maximum population.

My allies are not betraying me because we are all fighting the same unchivalrous foes. The Moors, Milanese, and the HRE are all a bunch of backstabbers and my allies are helping me fight them. Or at least not betraying me. This is important because my last attempt failed when everyone in the world stabbed me at the same time, and under my house rules, I could not execute prisoners and they kept coming and coming, over and over... there was no way to push them back without cheating.

It was a war of attrition avoided by being a chivalrous knight rather than a deranged berserker.

In practical games or against very very powerful AI, rep means nothing. Only house rules make rep mean something.