Have you seen someone about it? I had immense shin splints all of a sudden during training last year.
Basically it transpired that my feet had a weakness that made me pronate after about 8 miles. This meant that I was using different muscles and tendons in my lower legs which then caused me massive pain.
Ealing HM, pretty tough in places - lots of gradual hills, but a well organised event and one they don't over subscribe (my usual issue with races)
The route is not spectacular, but it's a good challenging run at a decent price.
On the opposite side I'd avoid run to the beat. I have not personally had any issues, but many others have including last year a bottle neck that destroyed some people's times. It is also very expensive...