Matt,
My opinion on the letters:
Personally, I think the letters you send out should convey your own voice, not anything canned.
Your letters should be
1. professional
2. eye catching- do something to make your envelopes look different from the other investors that will surely contact them
3. positive, but should create a sense of urgency ( mentioning the auction date is a good idea)
Create a spreadsheet that shows your success with each letter sent and make adjustments to see what works the best.
Gregg