Eh ... it's hard for me to put a definitive answer to this.

Generally, at least once a week I'll push really hard on my way to work. There's less traffic so I know my time will be better. It gives me a chance to measure myself against where I was earlier in the year. Early in the week my legs are fresher too. That pretty much defines how I'll ride on any given day. If I feel good after a few minutes of warming up, I'll chase the rabbit. It's pretty rare that I push hard all the way home. A lot of times I'll push pretty hard when I'm on the MUP if traffic is light. On the second half, when I'm on the surface streets, I don't push as hard. Today I had crazy headwinds, so it was pretty much gear down and suffer all the way to work. Tonight it'll be an easy ride home (provided the winds don't do a 180).

Basically I mix it up to keep things interesting. I also base my effort on how much work frustration I need to take out on the bike