Sluggish "Speed Workout"

I have mixed feeling about today's "speed" workout on the track. I ran 2 x 800 meters, with 5 minutes rest. The first was 2:42.5, the second, 2:44.8. The original plan was to run the first one at target mile race pace (around 2:38), then rest then run the second one all out as a time trial, whatever pace that ended up being (hopefully about the same as the first). However, I was several seconds off today. Perhaps I should not do speed workouts the day after my weekly long run. Yesterday's run was 7.3 miles at an 8:42 per mile pace, or about 1:03. Last week I had a great speed workout, but I only ran an easy 3 miler the day before, as I was planning on running a race the following day. I decided not to race, but therefore, my legs felt quite fresh for the workout.