I’ve done a lot of research into high efficiency speakers I would consider buying over the years. Here is the skinny:

Price shows as ~$4500. $500 more than III. Reviewer says in essence a clear difference in sound with good recordings due to midrange driver and crossover.

Would have to hear a/b to know for sure. Of course the differences as stated in the article would seem to make the additional cost a worthwhile investment. Probably worth more than $500 as described.

I’ve liked Forte III when I’ve auditioned off good modern SS amplification. Too big still for my use practically at present time though.

If I had a tube amp and need for the high efficiency...I would probably lean towards these as a cost effective and nice looking option. This is Klipsch Heritage line which has historically always been all about tube amps. Forte came later in 80’s but only available for a few years originally so apparently not a big hit back then. Tube gear has found a niche since then. Volti Razz is similar and $4999 so that is another strong option.

Tekton is also a cost effective option to consider in this league for tube amps, but not nearly as efficient as these Klipsch Heritage series horn based designs though and then there is the aesthetics...totally different.

Neither Klipsch or Tekton truly an "easy load" in general from what I read so performance and sound may still vary from amp to amp. I’d lean towards Fritz Speakers for that (an easy load). Those are less efficient but a very easy load and I have heard sound wonderful and plenty loud in a modest size room off a flea power set amp...a most impressive feat.
Can't wait for mine to arrive.....was about to pull the trigger on IIIs, but they were out of production so I put deposit on IVs....
I bought the Forte IIIs a month ago, and they are amazing speakers in my multi-use room (35 ft x 18 ft). I have them powered by Classé CP-800 and CA-2100 combo ... magical and very musical. My music collection has never sounded so good, period! Last night I saw the Audio Advice YouTube video on the Forte IVs and decided to contact my dealer to see if they would do an exchange given how recently I got the IIIs. They agreed and now I have a pair of the IVs on order. Music already sounds very real and live with the IIIs and I’m expecting the IVs to be even better. I’m really looking forward to it.
No kidding.  Good dealer and almost perfect timing (you got the use of the III for a month plus your wait time for the IV's).