For some great suspension advice, google Bruces suspension. He has very informative right ups on setting your suspension and is available to discuss. He is an advocate for the straight rate vs progressive springs though. He will be able to tell you what preload to begin with. As I mentioned earlier this is very important on 04's(and I believe 03's) as these shocks included a top out spring internally. If too much preload is set, this doesn't allow this to function correctly. Getting the correct spring is important.
I'm so far behind I think I'm in first