RAM will affect speed of panoramas. 16GB ought to be fine for most purposes, but of course that depends on how many original images are being selected for your panoramas, and how big those original images are.
RAM is not the only thing that affects speed, depending on what tasks you are performing.
and certain tasks in LR are incredibly slow and painful such as creating panoramas
What other tasks are incredibly slow? The answer to that will determine if RAM increase by itself will speed up Lightroom. In particular, the new iMacs tend to come with 4K or 5K monitors, and these require lots of CPU power (and GPU power).
Thanks for the reply. Panoramas are really, really slow. Most of mine tend to only be 4 images at most but they take several minutes to stitch together.
Playing slideshows or more specifically, generating slideshows is slower than it used to be especially as I find that since upgrading my camera to a full frame Canon 5D MKIII I have to set the quality to High in slideshows as otherwise the image quality is poor.
Generating the initial previews of newly imported photos is not slow as such but slower than it was on my old Mac.
Using tools like the Adjustment Brush is fine but if you want to view the overlay (O) it can take several seconds or longer to display it. Sometimes it doesn't display it at all and then you are in a cycle of pressing O and wondering if you've now just turned it off or on again.
I'm not in front of my iMac it at the moment but from memory I think it's a 3.2GHz Quad i5 27" and is definitely either 4K or 5K
More pixels in the monitor means that the CPU has to work longer and harder to do these things. Larger photos with the 5D Mark III means that the CPU has to work longer and harder to do these things. I'm not sure what 3.2GHz Quad i5 means, but that doesn't really sound like a fast processor. I know Apple wants everyone to think that its new iMac computers have a very fast processor, but I am skeptical, it might be fast for lots of purposes but it doesn't sound fast for Lightroom purposes.
It's difficult for anyone to say what upgrading the RAM on your computer would do to improve performance because (I think) every computer is unique. For instance, on my ancient HP Pavilion computer which will only accept 8 GB of RAM I have been able to stitch as many as 24 24 MP raw images into a single panorama in about 6 min. Smaller panoramas only take a few seconds. I seldom participate in these performance discussions because it seems that if performance is an issue then it's something that each individual must sort out for that particular computer. It doesn't seem to be specific to any operating system. I know, it's weird.