Even easier level to do this on is the Robot rampage level of arcade mode, only the massive bipedal and normal size ones spawn, 21 in all 4 of which are the large ones, you get a maxed sword and the extra is half speed on the enemy.
Essentially the tactic is the same as the other two mentioned but this will take you around 1:30 with max combo anywhere from 350 plus.
The advantage of this levle over the killing ground is the sword allows you to warp when you've been hit, making it far easier to keep the combo going rather than losing it due to getting hit.
Oh score i actually got was 121,357,150 you can get more if you avoid getting hit etc