Apple states: 'Dual display and video mirroring: Simultaneously supports full native resolution on the built-in display and up to 2560 by 1600 pixels on up to two external displays, both in millions of colours' (http://apple.com/au/macbook-pro/specs-retina/), but they don't state if a performance/memory hit would be encountered while using external displays. Technically, how many bytes make up a pixel on a 64-bit OS? Is it 8 bytes per pixel? (8 bits * 8 bytes = 64-bits per CPU cycle). I'm wondering if 8GB RAM will be enough for external displays while efficiently and comfortably running a heavy amount of programs and web browsing, considering Iris 5100 integrated graphics can take up to a max of 1024MB of System RAM, surely that can't be enough for the amount of pixels required on Retina (2560-by-1600 = 4 096 000 pixels) in-built display + 2x maxed out external displays (8 192 000 pixels)...which officially equals 12 288 000 pixels supported at any one given time (not taking into account the hidden 4K res ability), and I heard a third external monitor can be supported via the HDMI port as well which would take up more RAM for video memory. :/ If anyone has hooked up their Haswell (Oct-2013) rMBPs to an external monitor setup, could you please print screen your RAM usage from Activity Monitor; before and after the external monitor(s) were hooked up, thanks. I'm on the edge of staying with 8GB or going with 16GB, and this is the deciding factor! Cheers.