This is a good debate but it misses one point. The stretch method is better than the torque method only if the specific fastener has been designed to stretch a predetermined amount. This has to do with high quality and very pure metalurgy which can only be controlled by the manufacturer (ARP in this case). Also the reduced diameter of the fastener is one of the key factors in the stretch measurement. Most fastener manufacturers do not have the QC or even the ability to mass produce fasteners +/- .001" in length, so they use torque for a tightening specification.
ARP knows that when their rod bolts have stretched to the designed spec, they are at the peak of both strength and clamping force. Too little stretch and the clamping force is weaker; too much stretch and the bolt is closer to its yield limit under severe operational conditions. The guys at ARP will be glad to explain this over the phone and their on-line catalog does a good job at giving some technical details.
ARP | Catalog
I love this stuff.
Mark