Remember that according to Hotrod the changes in oil components was dictated by the car manufacturers. Here is what Shell says about Rotella:

"ROTELLA T Multigrade is a universal oil, meeting API Service Categories CI-4 & CI-4 PLUS for diesel engines, and SL for gasoline engines. Where the engine manufacturer recommends oil meeting either one (or both) of these Service Categories, or earlier categories (like API SF), ROTELLA T can be a good choice.

However, ROTELLA T does not meet all the requirements of ILSAC and API Certification Mark (starburst symbol) standards, sometimes specified for gasoline engine oils (in addition to API SL). These additional standards deal with fuel economy, and also limit phosphorus content (an element in all engine oils, but usually at a higher concentration in diesel oils). Phosphorus can affect catalyst activity in some exhaust emission control systems.

If your manual specifies only API SL (or earlier designation), then the catalyst is likely not sensitive to higher levels of phosphorus. If it also specifies ILSAC standards, using ROTELLA T may risk some catalyst activity loss.

Against the risks noted here, the advantage of using ROTELLA T comes from its more robust performance controlling engine deposits and wear. "

I don't know if I would recommend a high detergent oil in a sludge filled old flatty. Although I suppose if the detergents slowly cleaned up the motor it would be great -- I would just fear that it would loosen the sludge in the crank and plug it. Are you running the Rotella in a rebuilt flatty or an old runner? I think it would be interesting to find out how many people run detergent oils in old running flat engines without trouble.

Since I will rebuild mine I will run a multi weight detergent oil, and just because of the cost of parts on this thing, I probably will run a synthetic like Rotella, but I have had good luck with regular oils also. I have about 300,000 on my '76 F100 302 (rebuilt once with new pistons, and bearings, but still has the original cam and lifters).