In Japan the most referred effect of Russo-Japanese War in navy men-of-war was the effectiveness of armored cruiser/battle cruiser. In a sense, these types made an epoch after Sino-Japanese War.
The main naval battle in Sino-Japanese War was Battle of the Yalu River (1894).http://en.wikipedia.org/wiki/Battle_of_ ... iver_(1894
In this battle both side prepared the largest gun they can afford but at large they were ineffective (in accuracy and recharge time). On the other hand high velocity guns, including those from poorly protected cruisers, made a fire on wooden Sino ships and deprived armored ships of combat readiness by damaging anything on board.
Armored cruisers ordered after this war were in general thinly but wholly armored to prevent fatal damage from smaller calibre guns. Japan deployed 4 BB and 8 CA into the Battle of Tsushima. Japan had lost 2 BB (Yashima and Hatsuse) by then.
Both side already prepared the coordination of fire on each ship; that is, unified the aim of guns (distance, direction etc.) on each ship. Japan used the Barr and Stroud transmitter and Japan-made copies along with voice tube, blackboard, and of cource messengers for communication between the brdge - gun group leaders - each gun. Eventually poor training and heavy damage prevented Russians to coordinate fire and they must let each gun to fire at will. Coordination of fire in each ship was a prerequisite for Dreadnaught - the dealer of accurate outrange fire. So we can say a part of Dreadnaught concept was tested in this battle.
In Russo-Japanese War, however, they made cross-range battle. In catalog data, BB Mikasa's main gun had about 10km range and the latest CA Asama had guns with 18km range. But they did not have effective aiming system in such a long range. In the Battle of Tsushima Russians opened fire at the distance of 7km and Japan waited until 6.4km. So at least CA was not outranged by BB in that situation.
Japan divided 12 men-of-war into two fleet. Once Togo's own fleet, 4 BB and 2 CA, misunderstood the maneuver of Rozhestvensky because his flagship's ladder was damaged and looked as if he ordered the fleet to change the course. Second fleet, 6 CA, noticed Togo was misled and chased Russian fleet in original course at faster speed. Togo again returned to Russians and Russians confronted a pincer attack. CA contributed to the victory of Japan and various navies ordered their battle cruisers after this war.
In Battle of the Yalu River (1894) BB Dingyuan did not sink in spite of fierce crossfire from Japanese fleet. http://en.wikipedia.org/wiki/Chinese_tu ... p_Dingyuan
It was thought difficult to sink well armored ship by gun. To sink them, something must be done under the waterline. Mine, torpedo and even ramming. Especially Japan used various way to destroy Russian ships except ramming. Eventually Japan itself added the long list how a battleship can be sunk 'by gun' in the Battle of Tsushima making underwater damage by shells. I don't know how the balance between firepower and defense gear changed in this period, but the situation 'well armored ship cannot be sunk by gun' looks rather singular and temporal.