two guests on quad core - very slow performance

[sysadmin78]

On quad core linux host (latest vbox 3.2.10, or older OSE 3.2.6) I run one Windows 2003 virtual machine.

If this machine is idle there is high cpu usage, for which I googled the solution - that is running one small dummy virtual machine and pause it.

Thus I have
1) Windows 2003, 2048Mb RAM , 1vCPU etc, vt enabled, nesting pages enabled
2) dummy machine, no drive, just 32Mb ram, 1vCPU, paused

When running compilation on this Windows machine, it takes approx. 10minutes to finish compiling one project.
When running dummy machine in parallel, it takes an hour or more! Core usage on host is much smaller.

When I get more RAM I planed to add more real VM's to use more cores on the machine so this is a big issue to me.

Thanks for helping

[sysadmin78]

Problem is same even if I run another standard VM with little RAM beside Windows 2003. Pause or unpaused - no difference.