Personally I just track sales constantly. I know I don't want less than my smallest, so I look for 14TB and up. If I come.across an upgrade for the right price, I buy it even if I don't need it right now. The drive I replace moves to another array, so its not wasted. Hell I'm still using some 2-3TB drives in the (much larger in qty) backup array.

The only thing I'd point out with the DC is they may not even have the hardware in there - there's a stupid amount of money that is being counted against product not even installed (or even shipped yet) in the stock value game these narcissistic scumbags are playing.