Finally, some useful replies. Thanks all.
Revelate. Eric at Revelate was the one who gave me the reply to use two rear panniers plus full frame bag, handlebar dry bag setup, and cockpit bag. As I stated, the three lightweight bags would give me approximately 2/3 of the capacity of two additional panniers, which is what I am looking for.
Just use 4 panniers. Advantage of combination setup I am inquiring about would be saving weight on bags, presuming two panniers weigh less than the three lightweight bags, and saving weight of rack.
Reduce load. For me, getting load down to 4 panniers was an effort; 4 panniers, no other bags, nothing on rear rack. As stated, my requirements are for bicycle touring, on road, camping, cooking, on extended tours, lasting weeks or months.