My system finally arrived yesterday and I got things set up using ISBoxer with 5 characters, but I'm not getting the performance I expected out of it by any means.

If I have low detail on the slave characters and high details on the main, I get 30 fps (limited in ISBoxer settings I think) on the slaves but only 20-40 fps on the main, lower in major towns and cities. I was at one point as low as 13fps in Exodar!

I can get it up to nearly 60 fps if I disable shadows on the main screen but only outside towns as soon as I enter a busier area it drops back down. Changing the affinity settings to 0 & 1 for main screen and 2-7 for the slaves seemed to help marginally too.

Could resolution be an issue? With my current ISBoxer setup I think it is running all 5 clients at 1920*1200, which is 11.5 million pixels to render. I don't really want to change this though I like being able to swap the slave views into the main screen at full resolution.

What other settings changes and config tweaks can I do to improve performance?

I was expecting not to drop below 60fps at all on the main screen (Dalaran & other Major cities excepted) with PC of this spec, maybe with 5 clients running this is an unrealistic expectation?