Interesting topic. I just have to add my two cents here. What I have found with cast iron vs. teflon rings is this:
Cast iron rings are designed to grab the bore of the drum and spin in the sealing ring groove. If it is desired to use cast iron rings in your 200-4R, use a brake hone to true the sealing ring bore and impart a cross hatch pattern or at least a rough surface of some sort. Because the cast iron ring has a pre-tension to the bore, it is slower to react when pressure is applied and side clearance to the sealing ring groove becomes critical. Using a cast iron ring with line pressures up to around 210 psi max has shown normal wear on the iron rings. Above 210, say 250 psi, the iron rings tend to grab the sealing ring groove and spin against the bore of the drum. This is evidenced by rapid wear to the face of the sealing ring that contacts the bore. Clutch failure will soon follow.
Teflon rings are designed to grab the sealing ring groove and spin against the sealing ring bore. Hence the narrow face commonly found on teflon rings. Less area to allow the ring to grab the bore when under pressure. Because the teflon ring is not pre-tensioned to the bore as the iron rings are, when hydraulic pressure is applied it immediately slams against the sealing ring groove wall and because of its flexibility, contours to any imperfections of the sealing ring groove wall and the sealing ring bore, providing a much better seal than a rigid ring could provide. One of the draw backs of teflon rings is the chance of the ring wearing an aluminum sealng ring groove. Sometimes floating metal will imbed into the teflon and act as a lathe on the aluminum material. I have not noticed that being a problem in the 200-4R. Another is shrinkage. Again, I personally have not seen that as a problem either. I can say, I have seen enough worn iron rings in high line pressure applications that it is well worth the risk to use teflon in those applications. I also use 4L80E center support rings.