bit different now. SAA operate both 524H-Ts and CF6-80 powered 744s - ask them which they prefer. Cargolux switched from GE to RR and CR2 will probably tell you how they're getting on too
Air New Zealand and Qantas operate both RR- and GE-powered B747-400s, ask them which they prefer.
IIRC, Cargolux was the launch customer for the RB.211-524H-T which had a new core from the Trent 700. The original -524H had a lot of HP turbine durability issues, IIRC. The launch of the 524H-T was meant to address those issues. So, Cargolux didn't order the -524H-T based on proven performance.
However, your other example, SAA switched from Rolls to GE. And so did Qantas and Air New Zealand.
Aircraft residual value is a strong function of market presence. When there are significantly fewer RR-powered -400s than either GE- or P&W-powered -400s, it's inevitable the latter two will command a residual value advantage over the RR-powered -400s.