2 smash.bro
Your calculations were a bit lame...
i mean, carrier costs 350/250 plus 25x8(interceptors)/0 which is 550/250.
...then, for zerg all units takes the same time to hatch, because it all depends on larvae. If u have 3 hatcheries and want to make 9 ultras, or 9 ling pairs, ling will come out faster, but affter that, you all units are made at the same speed.
so lets see now, lets use 72 suplies for both.
12 carriers: 550/250x12 is 6600/3000 (plus expences on upgs and buildings)
and for zerg, u can make more defilers if u have more gas left, or some lings for consuming if u have more minerals left.
6 defilers: 50/150x6 is 300/900 (plus expences on upgs and buildings)
60 hydras: 75/25x60 is 4500/1500
so it is 6600/3000 vs 4800/2400 if we compare by supply. U could compare by money, which would probably show what is more cost-effective...
btw, most of the hydras would survive, because u know - dark swarm =] so even if hydras would cost more to counter carriers, it'd be worth it.