Here's an example:
Glenrowan in r7 in syd
Going down several class from Group 3 to Welter - rises 8kgs in weight.

I think its 4 grades lower Welter-Flying-Quality-Listed-Group 3.

In fact that race r7 is a good example of class/weights - have a look at all the runners.

If you want info on handicapping in relation to class, wins etc go to the Victorian Racing site.