Take things slow work?

Quite a few things to reflect back for today, but I thought this one is quite interesting.

Today I was running on treadmill and decided to gradually increase my speed as I run and see if my stability will be better. Usually I start off at 10'00" / km speed and stay there until I finish my desired distance. Which, until now, I always finish my run very exhausted. This time as I gradually increased my speed from 7' / km to 10' / km, I wasn't as exhausted as I used to be and felt that I can still go on for another 300m or so. When I came home and checked my time on nike+, surprisingly the time I finished my run this time was almost the same as I did last time, when I maintained the 10' / km speed all the way.

I doubt that I have improved my stability that much in just a week, because 3 days ago I couldn't even finish 2.2k while maintaining 10' / km speed.

So, what does the whole thing mean? I don't know for now, but I guess I'll try the same method again next time and see if this gradually-increasing-speed method will really help on my stability. It could also be a psychological thing. As I slowly increase my speed, I don't feel that much pressure that I have to maintain the speed to finish the run. So, it's probably mentally easier to take things slow, which then helps the body to sustain longer.