Many times people will mount their rear sets back as well as higher than the OEM pegs. One reason for this is, especially if you are riding on a track or very curvy roads, you can lean the bike much further down without scraping the pegs if they are mounted higher than the originals. Also, when making these mods, most people put more aggressive handlebars on (ie. clubmans or clip-ons) which puts them in a position that is leaning forward more, if you don't move the pegs back your knees will be in your chest (esp. if you are tall) and it is just not comfortable. When you change the position of your pegs by putting rear sets on, you also have to create a linkage between where the shifter connects to the bike and where the rear set is located. This task is easily accomplished with most bikes because the shift lever rotates front and back in relation to the front and back of the motorcycle. CX models however, shift left and right, and from under the bike so the linkage is a bit more complicated, but not impossible. There are plenty of people who have made their own linkages for rear sets on this forum and I'm sure they would be willing to share their secrets with you. I am getting ready to put rear sets on my cx so when I figure it out Ill post it here. I'm sure people would post some pictures of what they have done if you ask. Hopefully that was not too confusing of an explanation.
cody