General & specific training

I have a question which board users may be able to help me with that at first seems very simple.
It is - when does general training become specific?
For example, running would normally be considered specific training for middle distance athletes. However, if an 800m runner with a pb of 1.50 (55s per 400) runs 10 miles in 60 minutes (90s per 400) this would be considered a general conditioning exercise because the speed is so far from that of the race. As training exercises are conducted at higher speeds, when can the training be considered specific? (or can only work at exact race pace be so considered?)