Rift CPU Balancing?

Hi all,
so I have been single boxing Rift for last couple of months and only last week started to multibox again. Originally I was getting between 20 - 25fps in Meridian with my 5 toons on the same machine with main running medium and rest all on low. Since I returned I am hitting more 10 - 15 with all toons now on low. Looking at my cpu usage it seem pretty high and so I am wondering is there a change to the way the cpu balancing should be working? I am using ISBoxer and assigning 2 cores per account and 5 core using all 8 cores (i7960 cpu, 12 gig of memory, SSD and ATI 6970 video card).
Any got some tips to get the fps up? Or is it just the current patch that slowed things down?
Thanks for any help

I've played around with different core and video settings combinations and here's what I'm using right now with satisfactory results:

Core 1/2,7/8 - Slot 1, graphics Ultra
Core 3/4 - Slot 2/4, low-quality renderer
Core 5/6 - Slot 3/5, low-quality renderer

I have run my setup using low settings for slots 2-5 but found switching to low-quality renderer gives much the same appearance as low settings and gives significantly more fps on my slot 1 session.

Also, my experience is that the gpu difference between low setting and ultra is minimal while the cpu usage goes up tremendously. That's why I have 4 cores assigned to slot 1.