Maybe the 800's are a bit too long of a distance to get the results you are looking for. Try adding "strides" of 50 to 100 meter repeats, fast and hard pace, but not full out, with 100 meter recovery after one of your weekly runs. I have seen these type of intervals, along with "tempo" runs in many speed building programs. The tempo runs increase your ability to run faster for a longer time, and the strides assist form, fast twitch muscles, and leg strength. Maybe add some 200's in while you are doing 400's, and push your pace..and also, running some races finishing with a good "kick" at the end will help mentally and physically to build speed and endurance..try some running with a faster friend.. pushing your normal pace is easier with support! Check out some of the speedwork articles from RunningTimes..http://www.runningtimes.com/issues/index.htm.. Good Luck on speed building.. it is fun but hard work!