Isn't that a symptom of your camera's RAW file format containing only a small preview JPG, rather than a problem of PM in combination with a retina screen?
(I have no idea what camera you use so obviously I could be very wrong!)
I mainly use a 5Dmk3 (which embeds a full-size preview JPG in its RAW file) and don't have any such problem zooming to 100% in PM's preview, or whizzing through a folder of RAW images previewing at 100% or fullscreen.
My 1Dmk3 RAW files contain a smaller preview JPG; but it's still bigger than my screen size so it's still sharp. If I wish to view a full-size preview (to examine critical focus) I simply hit 'Q' so that PM allows the MacOS to render the RAW file for preview (it slows things a little, but it's very usable).
Have you tried setting PM preferences to let MacOS render your RAW files' previews? It may slow things down unacceptably, but it may be worth experimenting with to see if it's workable.
Other possible solutions could be:
- Convert RAWs to DNGs, which contain full-size previews.
- Shoot RAW+JPG and set PM to use just the JPGs for previewing purposes (it will still hand-off the RAWs for editing).
- Don't use PM!
Apologies if I'm stating mind-boggingly obvious stuff that you've already considered and rejected.
Have you contacted
Camerabits concerning this problem? They're extremely helpful.
(If you don't use a Mac then all that guff about getting the OS to render the RAWs for previews is irrelevant.)
Huge apologies for dragging this a wee bit off topic.