I normally do 100 mile weeks between commuting and sport rides, and I find that the thursday/friday commutes can really blow out my legs if I push too hard. I know the back half of my return commute is all lights and city traffic, so I normally push for the first 6 miles, then loaf along for the last 4, it gives me a chance to recover and relax a bit, pushing door to door is fun, but I still have to walk upstairs when I get there.