If your doing 7:30 for 10 milers pretty easy then your right....you should certainly be able to go lower than 50 min for 10K. I can see why your frustrated (been there myself). Do you use a HR monitor in your training and races? If not, that can reveal some interesting things relative to your overall output. You might be going too hard on the bike. After knowing a bit more, I don't see how incorporating more bricks (intelligently) can hurt much. Keep in mind you can bank some hearbeats on the bike and not sacrifice too much time... Something that might reveal some benefits in your bricks would be experimenting with different cadences or the intensity in your pedaling. cadence is obvious but pulling hard with hams and not pushing as much with the quads can lead to a very different feel off the bike. It's never easy to transition into free-flowing fast running. Some of the folks I train with promise themselves they will pedal a very high candence for the last mile and no matter what...take it easy for the first 800 yards in the run.