I'm not sure the details on mixing RAM types these days, particularly with ECC/non-ECC. I have the stock 27" i5 iMac (so presumably 2x2GB chips). I have 2 1333mhz ECC 1GB chips (http://www.eworldsale.com/samsung-ddr3-1333-1gb-128mx-72-ecc-memory_8764_43363.html) available to me. Would it work to pop those in to the 2 empty slots in the computer or would mixing the types cause problems?