A hook is important, but what is more important to a good sales letter is to createa personal touch. Connection sells not sales pitches or information. Too many people fill their messages with info, stats etc, then they get few replies back cause people open these and just delete them because it all smells of sales.
If you want to make an impression with return then figure out a way that makes your letter sound personal, use words like , help, assist, reaching out, ect and express how your "personal experience in this industry" gives you an ability to help their business and that you would like to schedule some time to talk a bit more with them about how you can help them.
Make your letter sound more like your wanting a job with their company (but dont say that, just have that attitude) instead of providing a service.