Hi,
I have the luxury of having two sites that are the same size. Therefore vCenter was configured with linked mode with multi-site SSO (sharing the same SSO instance) and as both sites are sized the same for failover reasons - I didn't have this problem!
I'd be happy to be corrected, but I believe you want to size your vCenters for the local site they are managing. So in this instance, deploy your APAC instance which is for "small" and your USA vCenter as "Medium" or "Large" depending on where you fit in. The SQL requirements, are again, for your local vCenter requirements.
Linked mode is essentially a cool feature that let's you manage all vCenters from one vSphere client. There are plenty of good docs available on linked mode, I used the main VMware KB to get me going though.
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Regards,
Ryan
vExpert, VCP5, VCAP5-DCA, MCITP, VCE-CIAE, NPP4
@vRyanH
http://vRyan.co.uk