Just a note on warm weather and computers...
The problem is exacerbated by latest computers getting all glue up and stopping average users from cleaning them. Two iMacs felt distinctly hot when touched at the back and when opened up didn't look particularity dirty. However the cooler fins (invisible behind the fan cover) have been heavily soiled and a compressed air blast produced a cloud of filth spewing in all directions! When everything was reassembled the processing speed returned and the computer back felt cool even after another hour of use.
If you have a similar issue then get in touch with your favourite local IT tech and get it cleaned! It is not only software filth that slows down your IT, the old-favourite dirt is still at it too!