Given that all hidden powers have a power of 60 now, doesn't this mean that certain hidden powers can be achieved with better IV spreads? In particular, is there a post on-site (or elsewhere) that has the new "ideal IV spreads" for each hidden power type?
I'm not sure if someone has it in a nice, neat place. But you can just use the old ones, here's why and how.
(1) The move type of HP is determined by a formula that concatenates the least significant bit of the IV into a 5-bit long string. What that means in layman's terms is that only the *parity* of the IVs matter in determining move type. (Parity of an integer is whether it is even or odd.)
(2) In previous gens, the power of HP would then be determined by the specific IV values.
So you can just use any chart that shows the best possible IV spread for gen 5 HP. All you have to do is keep the parity of the IV the same to preserve the move-type. For instance, in gen 5, the best possible IV spread for a max power Fire-type HP is
31 HP
30 Atk
31 Def
30 Spd
30 SAtk
31 SDef
This remains the best possible IV spread for Fire-type HP in gen 6. However, if the pokemon is special attacker, you may not want a 30 Attack IV since it does not minimize confusion and Foul Play damage. Or maybe you want to make a Trick Room pokemon, so it needs to have the lowest possible Speed. In that case, you can choose any other IV as long as it has the same parity (even or odd) as the "optimal" IV. So in this case, a 0 Attack IV would still give a Fire-type HP, as would a 0 Speed IV (or both). That's because 30 and 0 are both even integers. Similarly, a Defense IV of 1 would also give Fire-type since both 31 and 1 are odd.
Essentially, in this example, Fire-type HP is determined by
HP=Odd
Atk=Even
Def=Odd
Spd=Even
SAtk=Even
SDef=Odd
Now there *are* other parity combinations that also give Fire-type. But this is the parity combination that gives the highest IV total. There well could be a parity combination that allows you to have, say, 0 Atk IV and 31 SAtk IV (in this example, we have to settle with 30 SAtk IV). But if you're not a mathy person, then it's not really worth figuring it out whether it's possible to get that extra IV point.
I would just stick with the general rule of matching the parity of the old optimal IV combinations.