I've experimented with 87, but the car doesn't like it a whole lot once temps get warmer outside. It bogs from a standstill quite a bit with the AC on. I have found that it likes 87 from the Exxon up the road, but other times I've tried it, it ran like complete crap on other brands. Hesitation was seriously bad.
I usually use 89 octane and feel that my (untuned) Cruze performs just fine on it, or in the peak of summer when it's 90-100 out, I'll use 93. Same reason...that bogging with the AC on is due to timing being pulled because of pre-detonation. It can be downright dangerous trying to pull out into an intersection and the car just won't respond like it normally does.
For me, there is no noticable MPG difference between 89 and 93, but there is a ~4 highway MPG difference between those crummy 87 tanks and 89.