KVM is meant to be much closer to bare metal performance but doesn't have (at the moment) the all inclusive, easily managed from one console, turnkey solution to massive virtual installs at the datacentre level. If you need to be able to remotely provision VMs and move them whilst live from one centre to another whilst upscaling them then you will probably need to go with vmware. If you have got the
Mike,
Are you familiar with any of the tools listed here
http://www.linux-kvm.org/page/Management_Tools
e.g. Proxmox, ConVirt, OpenNebula, Ganeti, openQRM? Comments?