Cross Training Plans and Today's Hills

While training for my marathon this time around, I plan to do more cross training.  I usually have two easy days of running each week, so I plan to ride my bike on those days.  I'm hoping that will prevent injuries, while making every run count.  TrainingPeaks says this about cross training:

On easy days, cross-training should involve a sustained aerobic effort with an activity like cycling or using an elliptical trainer, for the same amount of time you'd spend on the day's mileage.

Yesterday I rode 7.27 miles in 47:51.  My plan was 4 miles easy, which should have taken about 40 minutes.  Some of that was downhill, so I think that's about right.

Today I ran hills and I mean, I RAN hills!

Mile 1:  11:14
Mile 2:  11:48 - this mile contains one of the "walls" in our neighborhood.  Super steep (10% average grade) for about a quarter of a mile.
Mile 3:  11:12 - this took me to the top of the neighborhood, but I still had a few little hills to go.
Mile 4:  9:31
Mile 5:  9:19  - the last half mile had two little hills that I pushed as hard as I could.

5.01 miles in 53:03, 10:35 pace.