I have 12GB RAM on my new iMac, which seems plenty to me. My download speed is 10 Mb/s.

In iTunes>Preferences, I have the option of a Small, Medium, or Large Streaming Buffer Size.

Sadly, I do not know which size would be best in my case. Your counsel most welcome.

It doesn't really matter until you use iTunes for streaming. If you have issues with the setting then, see if adjusting it (up) makes the problem disappear. Of course, buffer size isn't necessarily the only variable in play with a particular streaming problem, but it's good to keep it in mind when troubleshooting. FWIW, I set the buffer to Large and haven't had occasion to change it since.

About 80% of iTunes streaming I do is radio listening. The other 20% is done at iTunes U.

Presently, I have the streaming buffer set to "Large" and AFAIK, all is dandy. Indeed it seems these waters need no muddying on my part. So Large it will be.

Thanks as always-

Actually it's recommended to set it to small first since that results in streaming content starting the quickest. If you have glitches, then increase the setting as needed. The larger the buffer the slightly longer it takes to start.