How much smaller will my arms be after liposuction?

You need to be seen to determine if liposuction is an option for you. Liposuction works When the skin is in excellent condition and the arm is not very big. A brachioplasty is necessary to reduce excess skin in many cases.

Without an exam, it will not be possible to fully evaluate you and give you recommendations. Be sure to discuss your goals and concerns with your board certified plastic surgeon and consider the pros and the cons. Be certain your surgeon is properly certified.  I've attached a link where you can start your search. 

You probably can't find much information because we typically don't record our results based on dimension of the arms or circumference of the waist for example and I'm not aware of any study that has reported this data with arm liposuction. 
We tend to look at our results in a more subjective manner when it comes to liposuction of the arms and that is to increase the definition of the bicep, tricep and deltoids as well as obtain a flatter straighter line on the bottom aspect of your arm rather than a hammock shape. 
Ultimately we are more interested in the look of your arm after surgery than the size of your arm after surgery and that's why you can't find any good data or papers written about this.
Imagine if you are unhappy with how your arms looks after liposuction, but your surgeon said "oh yes sure it doesn't look that great, but hey, you arm circumference is 3 cm less then it was before surgery".