I haven't followed the instructions precisely, due to lack of time, but will answer anyway in the interest of avoiding self-selection bias. (I'm also not reading any of the other responses yet.)

I had heard of the case, but not seen any mainstream media reports. It was probably on one of the blogs I read.

I spent about 5 minutes looking at the "guilty" site, and about 1 minute looking at the "innocent" site. My first reactions to the two sites were:

(1) Wow, the "innocent" people aren't really trying very hard. Is this really the best, most passionate defense out ther? Is komponisto actually playing some sort of rationalist psychological game here, where the real test is to see if we notice how lame the defense is? Hmm, maybe not, because we are advised that it's ok to look elsewhere...

(2) The "guilty" site is disorganized, but apparently full of information. Or is it really? It mostly seems to be emotional reactions, not a description of what they believed actually happened and why. Possibly that information is on one of those fifty-zillion pages, but gee -- if my friend had been murdered, and I wanted to make sure that her killers were brought to justice, I would make damn sure that the facts were front and center, with as many sources as possible, and that the arguments were crystal-clear. Then I would get into the emotionalizing about how terrible this is. But hey, I'm a Vulcan*, maybe this is normal behavior for grieving humans.

(*according to some people, and sometimes I don't know how serious they are)

So, to answer the enumerated questions:

1. High, but with a large margin of error.
2. High, but with somewhat less large (but still significant) margin of error
3. Somewhat higher than #1, but also with an even higher margin of error -- he wouldn't be subject to "anti-American bias" (thus indicating that a guilty verdict is more likely accurate), but he also doesn't have any high-powered advocates fighting for him (a false accusation would be less likely to be challenged) and wouldn't enjoy the protection of being American (which is kind of the opposite of the "anti-American bias" claim, but matches what I have heard about how Americans are handled by foreign legal systems -- i.e. more carefully than locals).
4. Well, you've done a pretty good job of concealing your beliefs by the way you've couched the argument... unless the fact that the "innocent" site is so lame is a giveaway... on the other hand, you might have spent more time on the "guilty" site than I did, and found clearer reasons to either believe or distrust it. 60% likelihood?

There's the obvious conclusion of "white American privilege is the only thing supporting Amanda Knox's case -- but that would be extremely circumstantial, and has been proven wrong before (e.g. the Duke LaCrosse scandal took place just a few miles from where I live). I want to know what the real argument is, and I'm not finding it -- but I recognize that I haven't yet taken the time to do a proper search.

Okay, that's probably more data than you wanted for a largely inconclusive result.

UPDATE after reading some comments: I didn't notice that one of the links to the side on the "innocent" site had more information; my initial assumption was that they were all translations of the front page. Clicking on that link immediately takes me to a summary which seems much more clear-headed than anything on the "guilty" site, and actually gives a few facts involved in the case. A further link (clearly labeled) goes into considerably more detail.

After reading about a third of the detailed account, my estimates of Amanda and Raffaele's innocence goes up considerably (with accompanying reduction in the margin of error), along with my estimate of Guede's guilt.

However, before making a final determination I would want a great deal more information (e.g. recordings of the police interrogation, or transcripts, or whatever is available), considerable quiet time in which to ponder it, and a chance to ask any questions I might think of.