As nyet mentioned, you should be using a delta temperature difference for comparison purposes.

As you have it now, the percentage figures are units dependent. For example, 211 vs. 185 in Farenheit yields 12.32% drop. Fine. Now change the temp units to Celcius and 99.4C vs. 85.0C yields 14.5%. Change to Kelvin, and the difference would be 3.9%. Change to Rankine and, well, you get the idea.

You should be using temperature difference from ambient (since you don't have an intake temperature measurement). Now using the same example as above, there is a 211-75 = 136 degree rise for stoc, and 185-76 = 109 degree rise for IPP. Now the percentage is 19.9. That's what you should be reporting, and all of your figures will be inflated accordingly. With Excel that is a trivial matter to convert and update.

Second comment:

If the stock unit is more restrictive, then the exit temperature from the blow dryer will be higher since the air travels more slowly over the heating elements. This is an unknown factor and a second probe should be employed to measure this if you get a chance to do it over again. In an ideal world you would set the air flow and intake temp identical for both tests. Air flow meters are incredibly easy to fabricate btw.

It's a great experiment with your limited resouces and time. Keep up the good work, Sir.

(slightly edited 4:09 EST)