BrowserUk,
This certainly doesn't look like brute force to me.

First you get the words each letter appears in (regardless of how many times it appears). Then, you consider the top 8 letters based on how many words contain the letter but only allow each letter to appear once.

Your solution would probably be a lot faster if you also threw out any word from the dictionary that had repeated letter since I can't see how you would ever consider them.