Varun,
One need to take care of so many things to increase the PACE....whatever said above is true at the same time i would like to add couple of important subjcet to it....
1)Strength training is very crutial
2) Mike i am not very sure one can run at a high speed for 4-5 minutes....rather what i recommend is run at a high speed till you feel you are almost breathless and then stop...once the breathing about to normal start the process again...in a week you should do this only once.
3) cycling really helps to build your endurance and lung capacity in turn that helps for speed and for the longer run.
4) Varun also the point is what is your current speed and what distance you are focusing at that speed...and at any given point of time the right way of increasing is 10% of the either speed or distance more per week.