Long run comparisons... disappointing :(

I ran 29.13 km last sunday and I was curious to see the difference between that run and a long run that I did as part of my preparation for Reykjavik Marathon. To my surprise I have not improved that much, I have improved 4.37% in my pace and about 2% in my heart rate. It was quite disappointing, but I have time to improve as I have started to change my work out schedule. I am doing a lot more speed and tempo runs and strength training on my legs...