Bigger cog on the freewheel? Same size? Or bigger cog on the fixed?

Thinking about getting a freewheel (seems a shame to waste all those nice threads on the other side of the hub) and I could see how it would be useful for riding the long hills up around Tahoe. I was thinking that I'd probably go a tooth or two larger on the freewheel since you don't have to spin down and then it's easier climbing when it turns back up.

How do you flip-floppers do it?