Why can't I enable EVC on my brand new identical hosts?

I've tried to enable EVC on my cluster of IBM 3650s with dual quad-core E5440s but VC won't let me.

Any ideas why?  I know the Intel Flex-migration feature set is a requirement but do I need to enable that in the BIOS or something?

I notice in the admin guide the follow Intel processors are supported:

Baseline - Intel Core 2 (Merom), with specific processors Intel Core 2 (Merom) and Intel 45nm Core 2 (Penryn) - does this mean my E5440s (Harpertown) aren't supported?  After reading a bit about flexmigration - I have a nasty feeling it's only supported in the 7300 series chips so far.

Cheers.