What is a '5 star window'? If you mean a smart album set to display 5 star images then the album will remember the selection when you leave it and re-enter it.
Another way to find the alternate images is to select the 5 star image and do a Show in project. All derivative images will be in the same project.
There are other possibilities, use the split browser. Open a split browser and use one to stay on the 5 star image and the other to search for the other.
Probably others but those are what comes up off the top of my head.
I am in a project, I rate images I like 5 stars and when I'm done I choose to only look at those images within that project - in what I refer to as the 5 star window which results from my selecting it from a dropdown menu; so NO smart albums here.
But then I feel there may be images I overlooked and switch to Show All, from the same dropdown menu. I am now in a different window. Are you following?
So how do I go back and forth, using that dropdown menu, without losing my place in either window - either 5 star or Show All (whether I am in Browser or Split View)?
That's my quetion. No Smart Albums involved at all.
If it were me I'd make a smart album for the 5 star images. Like I wrote an album will remember its selection so each time you go back to it it will be in the spot you left it.
The display that results from filtering the browser is temporary so each time you you run the filter on the browser (which wll be each time you go back to it) the old selection is lost.
It should also be possible to do what you are looking for using split browser windows. Have one browser set to the 5 star filter and then use the other to search for the other images you are looking for. Never tried to use split browsers this way so not sure if they are both open on the same project if the selection will track in each. Don;t think it will worth it a shot.