I'd be inclined to check the splits from time to time, but mostly monitor your body and how it feels effort wise and where you are in relation to the people around you. As people fatigue and slow, you will tend to move up in the second half, even if your pace is steady. Since you are running within yourself, calculating splits should not be a strain, especially with a round number like eight and a half. I wouldn't focus on the mile to mile, unless you really want to. Some people use the lap function on their watch to get the mile splits, you can try that if you like. I prefer to break the race into buckets and secide how I will approach the early part the middle and the closing and have some cues I use to remid myself to stay focused and smooth. Being able to "associate" and think about the race seems to help rather than daydreaming.