Ask HN: Content or Wording on Beta Invites?

We are getting ready to launch our new service (www.nixty.com). We have a list of a couple of thousand people that have signed up for the beta. I'm putting together an invitation to ask these people to join and help spread the word. I'm wondering if anyone on HN has experience with crafting these invites? Sort of like A/B testing with invites; e.g., we did this and got X conversion rate; we changed this and it went up! Are there any specific recommendations/suggestions? Thanks!

Edit: Added the below example:

NIXTY - the service that empowers education for everyone! - is launching. You are receiving this email because you know one of the co-founders or you have signed up to be notified when the service went live.

NIXTY helps students save money, grow and excel. It helps educators make money, and save time and energy. Everyone who joins gets a free ePortfolio and access to over 200 video courses from the top universities on the planet.

Sign up here (hyperlink) and help us spread the word!

Thank you, The NIXTY Team