Well, comparing conventional configurations with canards is a good idea. We could look at it from another perspective, compare the Berkut and the Osprey GP-4 which have the same engine, a Lycoming 0-360. The GP-4 has a top speed of 408km/h, cruise 386km/h, stall 105km/h and a climb rate of 12m/s at 562kg while the Berkut tops at 410km/h, has a cruise speed of 397km/h, stalls at 110km/h and climbs 10m/s weighting 460kg empty. So the only ultimate physical background that I see is the one Autoreply wrote nice and clear, that you can't get more than the laws of physics allow. Yes, the Berkut is faster and yes, it cruises more efficently. But at the expense of a lower climb rate and a higher stall speed. And all those small differences do not seem that much of a superiority when you sum it all up, whichever concept it may be.The conventional configuration is ultimately efficient by purely physical background. The conclusion that AR-5 outperformed the EZ purely on reduced interference drag is also wrong. AR-5 still has some excess interference drag unavoidable in low-wing configurations. A far brighter example is Wittman W-10 Tailwind outracing Rutan LongEZ with the same O-320 engine and almost the same wing area.
The superiority of the conventional configuration stands on three elefants:
1. Ultimate span efficiency, even a possibility to get E>1 is now discussed.
2. Minimal trim drag, even with high Clmax and large negative pitch moment of the wing airfoil.
3. Minimal structural weight without compromises in PP 1 and 2.
The search for still better aerodinamic layout has produced a 3LS configuration. Indeed three lifting surfaces also have not helped to outperform the classics.
Now when it comes to 3LS configurations it seems the Sukhoi Su-37 is pretty dominant and efficent, outperforming all classics. Also, there were 3LS homebuilts that outperformed both the classic conventional planes AND the most optimized canards. Like in the case of the Beck Mahoney's Sorceress (BTW, does anyone have info about the airfoils of that plane?) which is an example that the same supremacy of fighters can be achieved in homebuilt aircraft. The question is only whether such a homebuilt can be more efficient than any configuration in all aspects? Not only in top speed or top cruise but also in climb rate, lower stall speed, lower weight with better structure, the whole nine yards. If the military has succeeded in that, why not the homebuilts..?