I have a project which includes clips shot in 1080 50p, and 1080 25p, all at 50Mbps .mov, the latter when using "ETC". I also have a few slo-mo clips, at 1080 24p 50Mbps.mov.

How best to combine these so that I get the quality of 50p, real-time, not slo-mo, whilst getting optimum quality out of the 25p clips and retaining slo mo on the 24p clips?

Ron

50p timeline. That will leave all the footage near pristine to the original footage. You can try a 25p timeline but that will throw every other frame of the 50p footage out or bland the frames. Either way the 50p footage will change e way it looks.