The "real world" reason you can do that with the Eclipse is called electronic fuel injection. Were that a carbureted build, it would act completely different. Also as you pointed out yourself, alloy heads are much better at dissipating heat, so there's another score for less detonation. I'm in the preliminary stages of a slant 6 turbo build, myself. I plan to try some unorthodox (read dirt cheap) timing control and I plan to make it work, even though some say I cannot. That just makes me want to do it even more and I will.