My understanding is, this comes more into the case when google sees multiple sites with the same content. They check to see if they are within the same class c address block to see if they may be the same publisher. All Class B and Class C mean is how big a block of addresses one subnet is.
Class B addresses were initially given to respected, or important organizations such as universities, etc. But there isn't anything that would make an ip address of a B Class better for SEO, as far as I know. Classless addressing is what's really being used now, and I see no real benefits of having a B address now.