Another twist

There is another factor to consider here. I have had the opportunity to use a 6L and a 26L brakestands, each with a full consist of all cast iron brake shoes and with a full consist of the newer composition shoes. Let me first say the the shoes are one of the biggest factors in how a train brakes.
The cast iron shoes have much more brake power when they are first set up (they are rel. cold). To properly handle a train with cast iron shoes and a 26L you really need to know the road (which you should anyway) and have some decent power to work against the train. The 7-8psi reduction that you get from a 26L will stop you really easy. If you make the same reduction on a like train with comp shoes, you'll need another 8-10psi psi to get the train to stop on level track.
The benifit to comp shoes is that they brake better once you warm them up. The cast shoes, if anything, brake less when you heat them up.
The design of the 26L fits very well with the lack of dirt from the diesel air compressors (comparitivly speaking of course!), newer brake valves with rubber parts, longer trains, and the comp shoes that are not as sensitive to a larger minimum brake pipe reduction.
It would take an lot of power to stretch brake a mile long train with a 10lb reduction and cast iron shoes.
Ryan