I have a 25 mile RT commute. My usual run is 5 miles. I find it a little hard to do both 5 days a week, mostly because of time. I have to pay really close attention to my body when trying to build miles running. If running 8+ miles in the evening I'm probably not biking that day, 10+ on Saturday means Friday is probably a rest day. Having said all this, warmer weather = wanting to ride everyday and sometimes only 3 runs a week. You have to listen to your legs.