Best speakers under $500? Fire away!

Wharfedale denton, new.  Superb cabinets, laid back and smooth sound, good soundstage, at this price no problem.

Your rebuilt 3020 should not have any trouble driving 6ohms 86db as you listen to normal levels. The 3020 was renown to drive difficult speaker loads. That’s what made it a best seller. I have had the 315 driving such loads and it was just fine (before the pre-amp section started to short... but that one was a cheap made in china).
I would definitely not limit my search by speaker efficiency if the goal is not too reach the highest db possible with the given amp. But I agree, the 3020 would be a bad choice to drive MMGs or, given the specs and reviews, the Elac.
Also, keep in mind that you can try for 30 days and return if it does not fit...

Have you considered focal 705?  8ohms / 89db 

with the dentons and wharfedale in general, you would not believe the quality of the cabinet, the grill,  and binding posts you get for the money.  
In terms of sonics, they are on the warm side, mellow, laid back, very smooth and zero harshness highs, easy to listen to.  I have them powered by a marantz integrated that is also warm and laid back, and I do not feel like it is a good combination.
They are not monsters of details and air, nor do they fill the room, but that is compared to my totem hawks. They image ok, soundstage ok.
In my room, they are good for low to moderate volume listening, toed-in on axis 8ft away.  If the 3020 sounds like the NAD integrated I once had, dynamic, punch in the lows and the highs, then it could very well be a good match.
The dentons need power, more than my totem hawks.

Just love small 2-ways 5 1/2 inch when playing at low to moderate volume in mid-field, love large 3-way 10inch woofers when playing moderate to loud volume in mid- to far-field... I.e. Kind of miss my vandys 2ce thnking about it...