As an example, let's take HMS Neptune (1909) as roughly contemporary to RMS Titanic, and say she struck the same iceberg at the same speed in the same location on her hull.
Would the impact have been equally fatal? Is her armor belt able to shrug off that kind of impact? If she were to get a roughly equal sized hull gash, how would her flood controls fare compared to Titanic's?
Titanic was laid down in 1909, and completed in April 1912; this makes her nearest contemporary in Royal Naval service the Orion class battleships. These were well-armoured ships. They had a 12" belt extending along much of their length. At the ends, this dropped to 6", and then to 4", with ~45 feet at either end being completely unarmoured. The side belt extended from the upper deck to 3 ft 4" below the waterline. Beneath this was a 'double bottom', protection against underwater damage formed from two watertight layers of steel with a gap between them. An Orion class would also have better subdivision. Titanic had 16 watertight compartments below the waterline. The Orions had 22. The Titanic's were not topped by watertight decks, allowing water to run over the top of them into the next compartment. On the Orions, the watertight bulkheads ran to meet watertight decks.
When Titanic struck the iceberg, she was likely travelling at her cruising speed of 21 knots, or slightly below. It's worth pointing out that this was the top speed for an Orion class, which would usually cruise at 18 knots. She struck the iceberg on her starboard side (right-hand side when facing the direction of travel), towards the bow. In the worst descriptions of the damage she sustained, a 300 foot-long gash was torn in her side, both above and below the waterline. It's not exactly certain to me whether the same amount of damage would be sustained by an Orion class ship in the same circumstances. The unarmoured bow, stretching 42 feet back from the stempost, would be vulnerable; however, the double bottom would likely prevent any serious flooding below the waterline. Inflexible struck a mine in the Dardanelles in 1915. This opened up a hole in her starboard bow; while smaller (sources differ, but the hole was likely between 15 x 15 ft and 30 x 26 ft square), and penetrating fewer compartments than the damage done to Titanic by the iceberg (though extending further inboard), it gives us an idea of how a British warship would have coped. Inflexible suffered significant amounts of flooding, with 1,600 tons of water entering the ship. However, because the damage was done to the bow, where there were no large compartments to flood, she was never in any danger of foundering.
This was important because battleships, especially before the lessons of WWI, were vulnerable to flooding if large compartments were opened to the sea. In 1914, the battleship Audacious struck a mine in the Irish Sea. The mine did relatively little damage compared to the Titanic impact, but because the hole flooded her port engine room, a very large compartment, as well as large compartments immediately aft of it, it proved impossible to save her. There were also problems with water seeping through penetrations in the bulkhead for ventilation tubes, voice pipes and the like, as well as through improperly tightened watertight doors. However, as seen with the case of Inflexible, as long as water could be kept out of large compartments, easily done with damage to the bow, ships were likely to survive flooding.