Multiboxing: Minimum System Requirements
Rough estimate of what you should at least
* 5 instances: 4-6 CPU cores, 5GB RAM, 512MB video card
You have 4 CPU cores (plus 4 HyperThreaded cores is good), 16GB of RAM and a relatively high end 1GB video card. You're good to go
Here's some tips that might help:
* Your SSDs will of course improve loading performance over standard platter drives. I would suggest that performance will probably be improved by having all of the WoWs on one of the SSDs, rather than splitting between the two, due to caching. Totally up to you, the difference may not even be noticeable.
* The 5870 should let you run High/Ultra settings on your main window. Keep the others at Low for performance reasons, but bump up specific settings you might want (e.g. projected textures are a must have, view distance)
* The default CPU Strategy is recommended for your i7. It'll round-robin the CPU cores and use your HyperThreading. You can alternatively select the strategy that assigns all the CPUs to all the game instances and rely on Windows to manage them, but the idea of round-robin is to minimize contention between the processes.