After: Decomission the old system

I'd re-deploy the old systems as report "processing" off-loaders and/or compute nodes.

Obviously they are pretty good machines, currently, seeing they run Oracle and MS-SQL. That way you could get more life out of the machines *AND* make sure the old system(s) go away...

Get rid of the old and augment the new at the same time. That way departments don't feel like they are being robbed, you could even dedicate the old machine to them for specific things, making them feel special.

All part of "Protecting the Company's Investment". Yeah... err... YEAH!