Canon 5D Mark III vs 5D Mark II Vs NikonD800 VsNikon D700

	Canon EOS 5D Mark II	Canon EOS 5D Mark III	Canon EOS 1D X	Nikon D700	Nikon D800/ D800E
Sensor (effective resolution)	21.1-megapixel CMOS 4-channel readout 14 bit	22.3-megapixel CMOS 8-channel readout 14-bit	18-megapixel CMOS 2-line, 16-channel readout 14-bit	12.1-megapixel CMOS n/a 14 bit	36.3-megapixel CMOS n/a 14 bit
	36 mm x 24mm	36 mm x 24mm	36 mm x 24mm	36 mm x 23.9mm	35.9 mm x 24mm
Focal-length multiplier	1.0x	1.0x	1.0x	1.0x	1.0x
Sensitivity range	ISO 50 (exp)/100 - ISO 6400/25600 (exp)	ISO 50 (exp)/100 - ISO 25600/102,400 (exp)	ISO 50 (exp)/ 100 - ISO 51,200/204,800 (exp)	ISO 100 (exp)/200 - ISO 6400/ 25,600 (exp)	ISO 50 (exp)/100 - ISO 6400/ 25600 (exp)
Continuous shooting	3.9fps 14 raw/310 JPEG	6fps n/a	12fps n/a	5fps 17 raw/100 JPEG	4fps n/a (5fps with battery grip)
Viewfinder magnification/ effective magnification	100% coverage 0.71x/0.71x	100% coverage 0.71x/0.71x	100% coverage 0.76x/0.76x	95% coverage 0.72x/0.72x	100% coverage 0.70x/0.70x
Autofocus	9-pt AF 1 cross type	61-pt High Density Reticular AF 21 center diagonal to f5.6 5 center to f2.8 20 outer to f4	61-pt High Density Reticular AF 21 center diagonal to f5.6 5 center to f2.8 20 outer to f4	51-pt 15 cross type	51-pt 15 cross type; 11 cross type to f8
AF exposure range	-0.5 - 18 EV	-2 - 20 EV	-2 - 20 EV	-1 - 19 EV	-2 - 19 EV
Shutter speed	1/8,000 to 30 secs; bulb; 1/200 sec x-syn	n/a	1/8,000 to 30 secs; bulb; 1/250 sec x-sync (est)	1/8,000 to 30 secs; bulb; 1/250 sec x-sync	1/8,000 to 30 secs; bulb; 1/250 sec x-sync
Shutter durability	150,000 cycles	150,000 cycles	400,000 cycles	150,000 cycles	200,000 cycles
Metering	35-zone TTL	63-area iFCL	252-zone RGB	1,005-pixel RGB sensor 3D Color Matrix Metering II	91,000-pixel RGB 3D Color Matrix Metering III
Metering exposure range	1 - 20 EV	0 - 20 EV (est)	0 - 20 EV	0 - 20 EV	0 - 20 EV
Image stabilization	Optical	Optical	Optical	Optical	Optical
Video	H.264 QuickTime MOV 1080/30p/ 25p/24p; 720/25p/24p	H.264 QuickTime MOV 1080/30p/25p/24p; 720/60p/50p	H.264 QuickTime MOV 1080/30p/25p/24p; 720/60p/50p	None	H.264 QuickTime MOV 1080/30p/ 25p/24p; 720/60p/50p/ 25p/24p
Rated estimated max HD video length at best quality	4GB (approx 12 minutes)	29m59s	4GB (29m59s)	n/a	20 minutes
Audio	mono; mic input	mono; mic input; headphone jack	mono; mic input; headphone jack	n/a	mono; mic input; headphone jack
LCD size	3 inches fixed 920,000 dots	3.2 inches fixed 1.04 megadot	3.2 inches fixed 1.04 megadot	3 inches fixed 921,000 dots	3.2 inches 921,000 dots
Memory slots	1 x CF (UDMA mode 7)	1 x CF (UDMA mode 7), 1 x SDXC	2 x CF (UMDA mode 7)	1 x CF (UDMA mode 6)	1 x CF (UDMA mode 7), 1 x SDXC
Wireless flash	No	No	No	Yes	Yes
Battery life (CIPA rating)	850 shots (1,800mAh)	n/a (1,800mAh)	n/a (2,450mAh)	1,000 shots (1,500mAh)	850 shots (1,800mAh)
Dimensions (inches, WHD)	6.0 x 4.5 x 3.0	n/a	6.4 x 6.2 x 3.3	5.8 x 4.8 x 3.0	5.7 x 4.8 x 3.2
Body operating weight (ounces)	32.9	n/a	n/a	38.7	31.7 (est)
Mfr. price	$2,499 (body only)	$3,499 (body only)	$6,800 (body only)	$2,199.95 (body only)	$2,999.95/ $3,299.95 (body only)
	n/a	$4,299 (with 24-105mm lens)	n/a	n/a	n/a
Ship date	November 2008	March 2012	April 2012	July 2008	March 2012/ April 2012

All these improvements make the 5DM3 seem like an incredibly attractive camera, with enough there to merit upgrade consideration for 5DM2 pros who can justify the not-inconsiderable expense. If you're price-sensitive, the D800 obviously looks better, but you've got to be a real rez-head to consider the D800's pixel count a serious advantage and that presumes you're not committed to a system already.
Along with the 5DM3, Canon simultaneously announced some new accessories targeted at the same class of photographer.

• Speedlite 600EX-RT ($629.99, March): This replaces the 580EXII at the top of Canon's flash offerings, finally incorporating wireless flash mastery. It supports radio or line-of-sight and five groups of flashes on 16 channels.
• Speedlite Transmitter ST-E3-RT ($470, March): This is essentially the 600EX-RT without the flash.
• Battery Grip BG-E11 ($490, April): Though the 5DM3 takes the same batteries as the 5DM2, the grip's been updated with a duplicated multicontroller.
• Wireless Transmitter WFT-E7A ($849, April): This adds a lot of the wireless and wired Ethernet capabilities that come built-in to the 1D X, including time syncing, FTP, EOS Utility mode, WFT Server, and Media Server capabilities.
• GPS GP-EP2 ($390, April): A hot-shoe-based GPS receiver that supports GPS logging.