You should have no problems running even more chars than this. I have a similar i5 4590 which does just fine with 10 instances.
Open up Task Manager with Ctrl-Shift-Esc and use More Details view.
See how much each instance eqgame.exe is using of cpu it should not be more than 10%. It is possibly you might need to edit CPUaffinity setting in your eqclient.ini file.
You can also use this to track down other programs that hurt performance or are just plain unneedeed. I like to run my bots lean and mean and I even cut down on search indexer
Download HWmonitor from CPUID:
http://www.cpuid.com/softwares/hwmonitor.html
This will show you bunch of interesting info about your hardware but most importantly will show you GPU utilization (at the very bottom). It should not be over 90% and on your GPU should be under 50%.
One simple thing you can do lower the load on GPU is use
/viewport command, I like to use
/viewport 0 0 320 240 on my alts. It gives me just enough visibility to see what is going on(just like old DOS games) and GREATLY reduces my GPU load and temperatures.
Here is an old thread on this:
https://forums.station.sony.com/eq/index.php?threads/the-viewport-command.28696/
There is a MQ2 plugin (which sadly RG has not compiled) which automatically makes
/viewport 0 0 1 1 to all background MQ sessions and then
/viewport reset
You can imitate this plugin with hotkeys.
Then you need to decide what FPS limiter you are going to use, there is one built in EQ through video options, there is one in WinEQ and then there is
MQ2FPS plugin. My understanding is that you only want to run one at a time and that Sony's FPS limiter is pretty decent so that is what I use(i disable the WinEQ one and do not use
MQ2FPS). I just set frame rate to 10 when minimized and 60 when maximized.
Ultimately, what you would want to do is have two EQ installations, one with all the bells and whistles and graphics effects for your main, and then a second one with most options turned off for your alts. This would be just two EQ directories (can simply copy files and then adjust settings).
Oh I also use Stickfigures=1 on alts, but that is because I find it funny. It helps graphics a bit too. Most people just disable unneeded Luclin models.
Here is one resource with tips on optimization:
http://forums.eqfreelance.net/index.php?topic=2958.0
Here is another post on optimization for an emu server but should be applicable for most things on live servers:
http://ezserveronline.com/forums/index.php?topic=2988.0