Replacement of Air Handlers in Home Attic?

Its already done, BUT: I replaced TWO Trane Air Handlers in my attic (2 attics) for a delivered/installed price of $4800. The were both 24 years old. One is a 3 ton and the other a 4 ton. The workmen took 7 hours total to install them and they did from what I could see an excellent job. The Salesman orginally offered a $5240 price but after negotiation, we agreed on $4800. One of my reasons for being receptive to replacement was that they were 24 years old and that they had a SERE rating of 15, whereas my two newer heat pumps were 13 and 12, I believe. Not sure the SERE rating of the old air handlers but I suspect 10. The salesman claimed "20 to 25% less in electric bills". By nature, I am skeptical of such claims but I couldn't fight the argument of old ac's plus advances in technology (theoretically). Did I do the correct thing and is the price reasonable or did I get screwed? The guy who installed it SAID I had a good price as he is the one who accepted payment. Will my breakeven be really some 7 - 8 years on this purchase also? Many thanks for concise observations.