At the moment I am using a combination of 2 x 8 GB 1.066 and 2 x 8 GB of self overclocking (2.133 MHz) 1.333 MHz RAM.
It's working without any issues but of course only at 1.066 MHz, but 32 GB in total.
Also 2 x 4 GB 1.333 instead of the first mentioned mixed with the others is working fine and it goes up to 1.333 MHz for everything, but only 24 GB.
And the stock 2 x 2 GB worked too together with the "2.133 MHz" ones and the other brand 8 GB 1.066 MHz.
Even all three in combination work.
So I think every DDR3-SO-DIMM not larger than 8 GB per module with max. 1.333 MHz native speed should work, even with faster ones if you manage to find the correct slot combination to slow down the not supported speed modules.
It could also be that you get beeps because the timing does not match, then you just need to switch the slots too.
Strangely my Late 2011 MBP is able to run that self overclocking memory at full speed with 2.133 MHz but my Mid-2011 27" iMac not if I only put those two in it.
Edit: Just found a bug. There is no Early 2011 27" iMac, in the betas before it was shown correctly as Mid-2011.
This is the best source if you want to upgrade your Mac:
http://www.everymac.com/systems/app...inch-aluminum-mid-2011-thunderbolt-specs.html
Edit Number 12: I hope you read it after it was finished.
My concentration is not the best at the moment.
