Yellow Letters vs. Professional letters for seller leads?

[Jonathan Brobst]

This post is to get advice from those who have tested both yellow letters and a more professional letter to generate seller leads. 

I am currently using yellow letter marketing and am wondering if sending a letter that is a little more formal might test better and net more calls.  I know I could just test this in my market and that any given market can be different from others but still want to ask to see if others have tried it and what there results were.  My observation thus far has been that most of my seller leads that call are fully aware or have the presumption that I am an investor.  If they have this notion, I wonder if they then view me or my company in a negative way since the yellow letter is so rudimentary.  I have thoughts of sending a letter typed on my letterhead with a business card stating we are an investment company who buys in cash and are buying in your neighborhood.  I would still use a hand written envelope to increase the likelihood of it being opened.   

Have any of you tested this and if so what have been your results?  If you decide to weigh in on this please let me know if you have actually tested this or are just giving your opinion (not that I don't value one's opinion but am looking for empirical data).