Ok, here is a concrete example/problem.
3 Sapphire 7970s:
$410
http://www.superbiiz.com/detail.php?name=AT-H7970CBMfr Part Number: 11197-03-40G
Engine Clock: 950 MHz
Boost Clock: 1000 MHz
Video Memory: 3GB GDDR5
Memory Clock: 5700 / 5800(Boost) MHz Effective
Max Resolution: 4096 x 2160
Connectors: DVI-I, DVI-D, HDMI, DisplayPort
Dimensions (WxLxH): 120.0 x 280.0 x 40.0 mm
$436
http://www.superbiiz.com/detail.php?name=AT-7970GHZMfr Part Number: 11197-12-40G
Engine Clock: 1000 MHz
Boost Clock: 1050 MHz
Video Memory: 3GB GDDR5
Memory Clock: 6000 MHz Effective
Max Resolution: 2560 x 1600
Connectors: DVI-I, DVI-D, HDMI, DisplayPort
Dimensions (WxLxH): 135.0 x 285.0 x 45.0 mm
$584
http://www.superbiiz.com/detail.php?name=AT-7970_6GMfr Part Number: 11197-05-40G
Engine Clock: 1000 MHz
Boost Clock: 1050 MHz
Video Memory: 6GB GDDR5
Memory Clock: 6000 MHz Effective
Max Resolution: 4096 x 2160
Connectors: DVI-I, DVI-D, HDMI, 2x Mini DisplayPort
Dimensions (WxLxH): 115.0 x 275.0 x 52.0 mm
I'm assuming the $410 one is the best choice, anyone one else have thoughts on the matter?