Yes, there is a big difference between "performance" and "specific performance", like there is big difference between "general shape" and "specific shape".
When we speak about top shape in specific competitions, we speak about the ability to reach 100% of the potential in THAT EVENT.
Under this point of view, for example, if you are a marathon runner, and you are able to improve your PB in 1500m two weeks before the marathon, this means YOU ARE NOT IN SHAPE FOR THE MARATHON, because your training went in different direction.
We speak about top athletes, of course, not about amateurs. In their case, it's possible that, increasing mileage at slow pace, and increasing speed with short intervals, they can be able to improve all their PB.
But the case of top runners is very much different.
The key of training is :
A) To identify his SPECIFIC TRAINING (specific because is directed to one specific event)
B) To increase THE VOLUME OF HIS SPECIFIC TRAINING
C) To prepare the athlete, using FUNDAMENTAL and SPECIAL TRAINING, to reach the above goal (to increase the volume of specific training)
Under this point of view, IN ALL THE EVENTS OF ENDURANCE, the specific training is something including various distances run at a speed between 95% and 105% of the speed of the race.
I want to give some example :
for athletes having a PB of 3'45" (1500, speed 15" every 100m, specific speed between 14"2 and 15"8 every 100m :
tests of 200m (28"4), 300 (42"6), 400 (56"8), 500 (1'12"), 600 (1'26"2), 800 (1'54"6) and 1000m (2'23") at 105%, stimulating specific speed,
test of 600 (1'39"), 800 (2'10"6), 1000 (2'42"2), 1200 (3'13"8), 1600 (4'21"2), 2000 (5'24"4) at 95% stimulating the Aerobic Power)
for athletes having 27'30" in 10000m (speed 16"5 every 100m, specific speed between 15"7 and 17"4 per km :
test of 600 (1'34"2), 800 (2'05"6), 1000 (2'37"), 1200 (3'08"4) at 105%, stimulating specific speed
test of 1000 (2'54"), 2000 (5'48"), 3000 (8'42"), 4000 (11'36") at 95% stimulating the Aerobic Power
long run of 6-10 km at 95% stimulating the Threshold
long run of 12-25 km at 90% (in this case 3'01"5 per km) stimulating the ability in extending the duration at the speed of Aerobic Power
In this training phylosophy, we say that EVERY SPEED FASTER THAN 105% OF THE SPEED OF THE RACE must be considered as SPEED, and is the "cherry on the cake", but is not the cake.
Of course we use also maximal speed, but never as one of the most important means of training.
One simple question : what do you do with a high speed, when you are not able to stay with the best athletes till last lap ? It's clear that, till when you are not one of the elite group in your distance (as endurance), if you want to be competitive the goal is to enhance the average of your speed, and this is possible increasing the Aerobic Power, not the speed.
Among athletes having the same level of endurance, the faster wins. But NEVER the faster wins, if his level of endurance is lower than the level of some other competitor.