The problem you're going to encounter is manufacturer's rate their parts (operating, not storage) for the die temperature, not the case temperature. Now, this is where it gets complicated: To determine the die temperature, you need to determine the power dissipated in the part, multiply that by the thermal resistance of the part, do the same for the thermal resistance of the part to the PCB board too, and also figure in the ambient temperature. Yikes! I know that's not the answer you are looking for. Point is, there's a lot a viables to factor in here and as Quench eluded too...some parts are better thermally than others.
In the end, if you think a part is operating correctly (i.e. dissipating the correct amount of power) and everything is working OK but just warm (maybe from a poor design), you can always try adding a thermal pad under the part which will help wick away the heat by lowering the 'case to PWB' thermal resistance. Look up 'sil pad' or 'gap pad'. Not the ideal solution, but it may help.
Sorry for the long winded answer.