So, I just completed the fan swap from the 10" Harbor freight unit to the Rikon 12" impeller. The purpose, of course, is to increase the available pressure to cause more volume flow.

The increased flow means more mass is being accelerated so more power is demanded by the fan. More power means more current to the motor causing increased temperature rise.

Higher winding temperature means shorter insulation life. Operating at the full load current (FLA) rating of the motor you can expect about 20,000 hours for the mechanical strength of the insulation to be reduced by half.

FLA and temperature rise are normally found on the motor nameplate. My HFDC (2012 vintage) has no nameplate. So, what's the FLA of my motor?

The power cord that comes with the unit has a 15A molded plug, so possibly the FLA is 15A. Maybe the 80% rule is respected and it's 12A. If you're really gullible you could believe the HF catalog claim of 2HP an use the NEC 430.248 value of 24A but I think your smoke detector would object.

Sorry about the rambling background, the question I'm really trying to answer is 'how much does the larger impeller shorten the life of the motor?' To do that I need to know the actual temperature rise of the motor windings as well as the temperature rating of the insulation.

For a variety of reasons I'm assuming a Class A (105C) temperature rating. We can discuss later but this post is getting too long already to do it now.

I applied different loads and measured current and temperature rise (resistance method) and got the following result:
Values in the chart above 16A are extrapolated.

Insulation life is usally estimated to decrease by half for each 10C increase in temperature. Actual winding temperature is ambient temperature plus rise plus a hot spot allowance of 5C (Class A, 10 for hotter classes). I find the following chart useful:

Of course, this applies if the insulation is Class A. If you believe it to be Class F then multiply the hours by 22.