$160 for 4TB = $40 per TB
$115 for 3TB = $38 per TB
3TB = 7200rpm.
4TB = 5900rpm
GREEN or RED WD usually 5400RPM.
This 4TB seagate should be very competitive on energy while providing better performance and cost per TB.
I believe 4TB with 1TB platters and 5900RPM is ~5watts. WD GREEN 3TB is 5.5 watts. 7200RPM Seagate 3TB is about 5.4 watts.
I'd guess the 1TB platters on the 4TB combined with only 5900rpm to be just under the GREEN or 3TB 7200.14.
Of coarse the 7200.14 3TB is just as cheap per TB and highest performance due to 7200rpm.
"Too much is almost enough. Anything in life worth doing is worth overdoing. Moderation is for cowards."