Anything up scaled by the studio to 4K will have been done by some pretty serious equipment, so it will look good, and I guess not many would be ab,e to tell the difference unless they know what they’re looking for.
As for telling the difference between Bluray and UHD, don’t forget that if you’re using a UHD disc downscaled to 1080p, it can still look better than 1080p Bluray, so the differences won’t be as apparent - for any meaningful comparison, you need to compare a UHD disc against a Bluray Disc.
When looking for differences, don’t look at close ups of faces - even DVD can look impressive with that sort of shot. Find long shots of landscapes or cityscapes that are in focus - the difference between small details like leaves on trees or windows on buildings will be immediately apparent. This is where DVD falls down massively.