So, I know this Apple article: http://support.apple.com/kb/HT6064 states not to mix UDIMMs and RDIMMs. Looks like all the 16GB modules are RDIMMs. Apple's own recommendations tend to be more stringent than what's tested out in the wild. Has anyone tried adding a 16GB to a 12GB (4GB + 4GB + 4GB) base config for a total of 28GB, and if so, what are your findings? Or is it preferable to play it safe and add two 8GB UDIMM modules (replacing one 4GB one) for a total of 24GB?