I have seen many city sieges now, and have figured out the best strategy for stage 2 of the rvr driven city in Warhammer Online. It is not complicated, and actually is very simple.
At first it seemed like the most logical strategy was to follow Volkmar since he was a little faster than the other Warlord. Destruction has soon caught on to this strategy, and it usually ends up with Volkmar dead when the two factions meet near the temple.
A new, and improved strategy that I have seen work perfectly is to not even follow your own guy. The best strategy in stage 2 is just to get to Engra Deathsword as fast as you can.
This strategy works best because it catches Destruction off guard, and they don't have time to set up a defense. You can usually catch Engra at the Outcrop along with all of Destruction with their pants down.
Normally we just burn down all the Destruction, and than kill Engra. After killing the Warlord it throws off Destruction, and they have no idea on what to do next. Basically you can just spawn camp them until Volkmar makes it safely to the gate.