Well, what actually happens when it is said that the cleaner, slower and heavier an airplane is, it is because (relating to the clean config) :
When an airplane is in slow flight at clean configuration, stall speed increases, and this is because the wing is needs a higher angle of attack to generate sufficient lift than when the airplane is in full flaps. The higher angle of attack is one of the reasons of the tremendous vortices created. When the flaps are down, the airplane doesnt need such a high angle of attack, because the difference in airspeeds below and over the wing is already high, of course air reaches the trailing edge at the same time. The need for a higher angle of attack when clean is to accelerate further more the flow of air over the wing to increase lift. A living and very famous example of a cleaner wing compared to other planes even when flaps are down is the 757, also the Concorde, and the Valkyrie (which was involved in an accident where a spot plane was grabbed by the valkyrie's vortices and the spot plane collided with the bomber) their wing is so clean that they need such a high angle of attack that creates superpowerful vortices. Now about that strong vortices are created on high speed cruise, they are not going to be as strong, because the airplane wont need big angles of attack because of the fast flow of air on the wings, if the airplane remains at a fixed angle of attack, lets say 10 degrees, if speed doubles, lift will be 4 times higher and this is why the airplane climbs.Am not saying that vortices are not present at high speed cruise but just that they are smaller, even an airplane with winglets will have vortices at it's tips, really small but they will still be there.