You can use Bridged networking https://help.ubuntu.com/community/KVM/Networking#bridgednetworking which allows your VMs to connect to outside world (default is User-mode networking which doesn't). You can find some more details here: http://www.linux-kvm.org/page/Networking
Do you really need to use KVM? Or your tests can be performed in any virtualized environment? Because I use Citrix XenServer and cpufreq scales the processors` frequency without problems.