I don't have any numbers for you. I did get a 2 hopper and 3 joey system at my parents house almost immediately after they were released. I noticed the Joeys were actually really hot to the touch. I changed them all from horizontal orientation to vertical orientation when I noticed it and they have been much cooler ever since.
At my house I have the newer Hopper with sling and 1 Joey. I stood the Joey up with the stand right away because I knew what it was like at my parents house. I have never noticed the newer Joey getting hot. I'm not sure if it's just because it is a newer unit or because it has been vertical the whole time I've had it. Sorry I can't give you any numbers but if you have your Joey laying flat I suggest you try to stand it up and see if that helps.
Yep my Joey can almost burn my finger if I touch certain spots on top while it's horizontal. If you can, run it vertical, it definitely helps with the heat.