Weight: system more important than sensor size?

I think that the issue is that you have to compare similar tech sensors. Canon,s current FF sensors are not quite on a par with this generation of Sony sensor. Personally I think that the very highMP count of the D800 is the way forwarded  . At low ISO it gives amazing resolution , while at higher ISO settings the extra detail allows  you to sacrifice some of the detail to NR . Obviously if high ISO is critical part of your work then the D4 is a more suitable tool.

With Sony now pretty much dominating the sensor market , with the best P&S ,one inch,mFT Aps and FF sensor. It is not a huge leap to assume that  the critical difference between cameras is down to sensor size ,assuming of course similar generation of sensor.All systems offer advantages and disadvantages , i love my mFT and my FF gear each doing a great job. I am now pretty much where I was with film years ago,with mFT being the fast lightweight option used for most subjects ( 35mm film)  and my D800 works like my old MF kit did for subjects where you are prepared to spend the time to squeeze out the very best you can,  RAW,low ISO,tripod ,critical focus,  and so on, landscape being a main subject .

We really are living in interesting times for photography.

Jim