As an alternative to buying ice you can let your wort chill in your fermentation chamber overnight. I've done this literally hundreds on times with no ill effects. It's kinda nice not to have to worry with aerating and pitching till the next am.
This is what I do. With my tap water temps, it is fairly easy to get the wort into the 70's with my little plate chiller--which will surely stop any DMS from forming. On a typical brewday I am done early enough, and the wort cools quickly enough in my kegerator-fermentation chamber, that I oxygenate and pitch the yeast right before I go to bed.
If I try to get the wort down to pitching temp coming out of the plate chiller, the wort is just a trickle. Like the OP said, the last 10 degrees is the problem.