I had the same problem, but I am using Logic 9.1.1 in 64bit and VEPro 64bit, all 8 cores are being used in Logic. Ok, the first core seems to go overloaded several times, but I think that this problem will be quite solved when VI Pro is being released. They optimize their software with each update, obviously. Everything what I did was to use both DAW's in 64bit and switched on the internal FIREWALL of Snow leopard. After updating to Safari 5.0 I found out that Safari got a big speed down, so I checked the system and saw that only the firewall could solve the problem because Snow Leopard was fully opened in network backdoors after 10.6.4. I am also working with an 8-core Pro with 32 GB RAM.
Try to switch on the firewall under security settings and see that the multithread tasking works better.
Give us an update here, please.