I will get canned or caned for this. A race comes down to energy and the effective use of energy. Aerobic energy is made 15 times the rate of anaerobic energy. The energy has to be generated on the run. After the available oxygen has been depleted the race has to be finished using anaerobic energy.
Thus a horse has a limited amount of energy. A limited amount of high grade energy and a limited amount of low grade energy. This has to be rationed throughout the race. Overcook it and the horse is suddenly having to run on low grade energy. Undercook it and the horse has waste good energy catching up.
So from a standing start a horse will quickly get up to speed at about 90% of its capability, it will then settle in the high 80%s for the shorter distances before a burst into 90% before flagging to the line as they switch to low grade energy. In longer races the horses will settle back to the 70% of capacity in the middle and then burst into the mid 80%s and come home on anaerobic fumes. About three quarters of the race is run on aerobic energy then the anaerobic energy takes over. Then the horse needs a week to rebalance.
When a horse from an outer barrier tries to get in front before the first turn using over 90% of its energy capacity it has overstretched its oxygen supply and lost its capacity to generate enough high grade energy to stay with the pack. It has lost its race. When a horse from an outer barrier slips in behind the pack to avoid having to go wide, it has to use extra energy during the middle period and not have enough to fight at the end.
The front runner is using the most energy. If the race is at the leaders pace then it can go wire to wire. If the pack pushes the leader past the ability for leader to still get oxygen to the cells then the leader will be overtaken. The horses behind are using significantly less energy. Backmarkers that can navigate through the pack rather than around the pack do have a chance.
Then you see the horses with the bigger hearts and lungs that can get more oxygen to their cells for a longer period. Class will always prevail.
So speed does count so does pace so long as one does not overstretch in comparison with the field.

__________________
"God made man in his image". He then went to great lengths to ensure that each and every person was unique. God then pondered and said "I will call these human, as very few will rise from the herd to be called individual" http://www.propun.com.au/racing_for...ttons/quote.gif