In a "ideal" world, what temp shud the cpu run at ???

Mine was running at about 77ish degree's earlier, and a few mates warned me it was running WAY to hot, but as its always run at this temp and the pc's is working fine i have ignored it.

Gave it a good clean out earlier, and its running at about 64 degree's now.

Is this ok or is it still running to hot ????

Been told it need's to be in the 40's ideally


Help pls