Its just doesn't feel like Total War if you can't sack Constanstinople at least once... In my game with the Sarmatians I took the easy(cheap) route and just sent all my Horde Horsemen and one of my two Cavalry Commanders of Genius chars. The smaller force lured them out to try and kill me and they got slaughtered on the field of battle. That allowed me to just waltz in, grab the loot, kill a bunch of people and walk out.