Ok, I understand your point. I'm just saying that fewer drives are easier to manage. You are almost certainly right that at least initially the price per gigabyte of the 5TB drives will be somewhat higher than the average 2TB, 3TB or 4TB drives and there are possible unknown reliability issues which is why I'd wait 6 months to a year for the price to come down and the reliability to be determined. At the moment based on the prices of Western Digital Green drives on Amazon (here in the U.S. and in dollars), 2TB drives work out to .0445 cents per gigabyte, 3TB drives .03822 cents and 4TB drives .0419975 cents. So yes, 3TB drives are the cheapest per gigabyte but a price differential of .0036675 cents per gigabyte is almost inconsequential and fewer 4TB drives rather than more 3TB drives is just easier to manage. Also in terms of reliability and warranty I would much prefer to use Western Digital Black drives which in my experience are more reliable than the green drives and in the 4 cases of failure I've run into 3 of the 4 were replaced under this drives 5 year warranty versus the two year warranty of the green series drives which I've had at least 5 out of warranty failures. But black drives are significantly more expensive than the green drives, right now prices seem to be 2TB .071475 cents per gigabyte, 3TB .068656 and 4TB .06759 (so in black drives the 4TB works out to the lowest per gigabyte cost) which makes the 4TB black drive about 61% more than the 4TB green drive which is just too expensive for drives used to archive data no matter that you get 3 additional years of warranty.
I didn't mean to imply that you were disagreeing with me so sorry if it seemed like it :-) I really just wanted to explain my situation and the use of these high capacity drives in my environment. Most of my desktop computers have two internal SATA drives (usually 2 X 2TB Black) and usually I have four to six unused internal SATA connectors in anyone of my workstations.