Hi, everyone, I just ordered a 5K iMac (after wanting a new MacBook and not getting one at WWDC) with 8 GB RAM and I'm looking to upgrade to 16 GB with Crucial. Should I get a 16 GB kit (2 x 8 GB) or should I just buy a single 8 GB and add it to what's there? When I last had an iMac I just bought a 16 GB kit and replaced the 8 GB with that but recall many people just adding that to the base 8 GB and getting 24 GB (but then some people talking about messing up timings, etc.). Also, this is the 18,3 iMac, right? I attached a screenshot from Crucial. Any suggestions or advice? Thanks!