I am mostly using the LX90, at f/10, as the guide-scope for the ED80, imaging at f/6.8.
I swap between the two DSI-IIs as needed, no longer using the DSI-IC as a guide camera now that I have the second -II (although it did a perfectly good job when I did use it).
I tend to work two PCs - a desktop one (1.3GHz, ancient) for gathering the actual images, and a P4 3.4GHz notebook for guiding (just because it gets the downloaded image processed much faster). I also use the notebook for the DSI-IC 'finderscope' camera - when needed.
I have regularly run all three cameras off the notebook, with no problems, even when guiding. And that is without any form of external supply or powered hubs (other than a mains supply to the notebook PC itself). I use high quality USB2.0 extension cables (5m) between the PCs and the top of the pier, and then 2m cables up to the cameras themselves.
However, I am about to add a pair of (powered) hubs to the top of the pier - just to simplify the cabling nightmare. This will also allow me to add a USB RS232 emulator to each hub - again to simplify getting the AutoStar connected to either PC. (Both PCs have 'true' RS232 ports - I would NEVER buy a PC that didn't have this level of 'legacy' compatibility - so this enhancement is purely 'cosmetic').