Hmmm, why all those tomcats? Are they all running Solr? I'm pretty sure you'd be a lot better off simply having one indexer and one searcher on this box. Give the searcher the most resources I'd guess. In fact, you'd be even better off offloading the indexing process to a different (perhaps less powerful machine) and running your searcher on this box, giving it a bunch of resources.
Here's what I'd do: Monitor the box (top on a *nix machine is a good first approximation) and see what your resource contention is all about. I suspect you're simply I/O bound since, if I'm reading this all correctly, this is all on one box and they're all Solr's. It's all sitting on one poor little disk, which is probably being beaten to death when it replicates to the 5 tomcats on the same box that are slaves at the same time. Try it with one slave rather than 5 for a quick test whether this is indeed an issue. Of course I may be mis-reading your setup entirely Best Erick
