Q:

Is the increasing availability of high speed internet pornography reducing sex crime rates?

Some early studies show that the availability of pornography does not increase the rate of sex crimes. 

Research on pornography has generally been of various types (Tovar, Elias, & Chang, 1999). Probably most common are studies that involve exposing experimental conditions of varying media to students or other subjects and measuring some variable such as changes in attitude or predicted hypothetical behaviors. Another type of research involves interviewing sex offenders and asking them of their experiences with sexually explicit material. And a third type involves interviewing victims of sex abuse in trying to evaluate if pornography was involved in the assault (Tovar et al., 1999). Surprisingly few studies have linked the availability of porn in any society with actual associated antisocial behaviors or sex crimes in particular. None have found a causal relationship and very few have even found one of positive correlation.
What sorts of actual behavior research data had the Commission and Surgeon General been reviewing? Findings from national studies were available from federal surveys and reports such as those of Kupperstein & Wilson (1970) drawing from U.S. Federal Bureau of Investigation Uniform Crime Reports. There were as well many other localized and more narrowly focused studies. Considering the interval from 1960 to 1969, Kupperstein and Wilson found, with some exceptions, while pornography became increasingly available, there was an overall decrease in sexual offenses.

In fact, many studies show the availability of pornography appears to reduce the rate of sex crimes:

Diamond and team looked at what actually happened to sex-related crimes in the Czech Republic as it transitioned from having a strict ban on sexually explicit materials to a situation where the material was decriminalized. Pornography was strictly prohibited between 1948 and 1989. The ban was lifted with the country's transition to democracy and, by 1990, the availability and ownership of sexually explicit materials rose dramatically. Even the possession of child pornography was not a criminal offense.
  The researchers monitored the number of sex-related crimes from Ministry of Interior records -- rape, attempted rape, sexual assault, and child sex abuse in particular -- for 15 years during the ban and 18 years after it was lifted.
Most significantly, they found that the number of reported cases of child sex abuse dropped markedly immediately after the ban on sexually explicit materials was lifted in 1989. In both Denmark and Japan, the situation is similar: Child sex abuse was much lower than it was when availability of child pornography was restricted.
Other results showed that, overall, there was no increase in reported sex-related crimes generally since the legalization of pornography. Interestingly, whereas the number of sex-related crimes fell significantly after 1989, the number of other societal crimes -- murder, assault, and robbery -- rose significantly.

If the basic availability of pornography, in any form, reduces the rate of sex crimes then I think it is logical to assume that easily available pornography from any home computer in the world should show an even more pronounced reduction in sex crime rates. Consider the current explosion of internet video content (YouTube was founded in 2005) and the prevalence of high speed internet versus the slow dialup modem connections that were common in 2000.
I'm specifically interested in recent studies of high speed internet pornography. What citations and studies are out there to support (or disprove) this theory? 

A:

This is a classic case of correlation does not imply causation.
One study found that high speed internet access reduced rape. But they couldn't find evidence that porn on the internet was the cause, just high speed internet access. So this is just a correlation between 2 data points.
A more recent study suggests that access to high speed internet increases the numbers of sex crime reports. Not the number of crimes, but the number of reports. This suggests that victims are more likely to report the crime if they have high speed internet. But again this is simply a correlation between data with no obvious or direct cause.
If there is a link there's no direct evidence for it yet. Part of the reason why might have something to do with the fact that porn does not always equal sex crime and that often sex crimes have very little to do with sex (see also this).
EDITED To include citations about sex crime motivations.

A:

This paper by Anthony D’Amato from 2006 deals specifically with the correlation of increased internet access and decreasing rape.
This is probably the most relevant part:

Four states with lowest internet access Increase in rape of 53%
Four states with highest internet access Decrease in rape of 27%

It's also correlational and he admits as much in the paper, but I thought it deserved to be mentioned as well.

