Is there any difference in performance when moving from slave to slave?

For example if I had the following slave sites.

- Homepage
- Jomsocial Profile
- Kunena
- and maybe 50 or so other slaves sites.

if each slave site had a forum link that brought them to a specific section of the forum and another link that brought them to their jomsocial page they would be bouncing around subdomains a lot. Does this effect performance?

I could share the forum with the slave sites, but if it is a large forum, is it better to have it on its on sub domain? I am also thinking of easy ways to mange these sections and figure if it is all on one domain under one forum, it would be easier. There would be no link to the forum itself just link to sections. Trying to avoid having to load a large forum and just show the section the user is requesting.

what would be the best way to set this up?

The performance is mainly related to the DBs.
Depending on the environment, sometimes, you have DBs located on different servers than the HTTP server.

The performance must be considered moreless like if you sum the total of hit on all the websites. The overhead of JMS is minor till 1,000 websites on the same server. Over 1,000 websites some specific setup might be necessary to speedup the processing.

If each website have their own DB that are located on different server, the performace is mainly related to the external server.

So the question is mainly related to the number of websites.
50 websites is very small.

We have few installation that have more than 1,000 websites and also one case with more than 10,000 websites.

You must better think in terms of what do you think if you put 50 standalones joomla on the same server with the traffic that you expect.
If you think that they can work without perfomance issue, this should be similar with a single Joomla and JMS.