If you us this useful tool:
http://www.touchgraph.com/
you will see how easily google can pick up a relationship between sites. It's widely acknowledged that direct reciprocal links are deemed less in value than oneways. Triangulating links, as you suggested, is a good idea to avoid this, and with 5 sites available (very good if all on different IPs) you can certainly mix things up.
It now depends on the relationship of your various sites and how many links you wish to move between sites. page to page it makes better sense to have one site liberally linking to a variety of pages on the next - and pass it on. Mixing up your anchor text is also important - basically, put the effort in to hand make each link on each page rather than introducing a site-wide generic link. Also throw in a few links on some of the pages to other sites (that aren't yours), so it all looks nice and organic.