My point was that average time commuting is not so much about strength and speed as road conditions. You are no slouch, you have to be going at an exercising pace to hit 12 - 14 average, you have to go much faster on the bits you can to push it up. (which town/city do you commute?)
On top of that, for me, anyway, I found that chasing a faster average gave me a goal, but also made me take more risk quite apart from the automatically higher risk that comes with added speed. Not for everyone, I understand, but chucking the computer made my rides happier.