Server CPU's: How much does L3 cache size matter when it comes to virtualization?

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http://serverfault.com – Performance-wise, how much does the L3 cache size on Intel Xeon i7 processors matter for virtualization functions? I'm picking out a Xeon 1366 Nehalem/Westmere CPU for a server I'm spec'ing to be a low end virtualization host for about 4-5 VM's. There seems to be a price divide between 4MB L3 Cache and 8MB L3 Cache. How much performance would I get out of stepping up to 8MB vs 4MB? (HowTos)