With what you're asking for, the 10 blade turbine upgrade for the 06 chassis would be my pick.
The 06 will spool a bit better because it's a smaller wheel so less energy needed to get it turning. The 03 exhaust housing and turbine is the same as what is on a PMAX and up to most standard S2 turbos. The 05+ turbine is a couple mm smaller, which helps with spool.
The gearing you have now is definitely a big change since your F250 was likely geared with 3.73s, so this F450 wouldn't react exactly the same even with the same turbo....HOWEVER.
If you are already pretty happy with what you have and you're just looking for a little whistle and a little more performance, I would stick with the 06 turbo and just make the swap with the 10 blade turbine. At that point since the turbo is apart anyways and you're going to have it all apart, I'd also recommend getting a billet single plane wheel and having Charlie balance the whole assembly before sending it out to you. That way you just have to put it all together, align the marks, and you have a whole brand new rotating assembly in your turbo that's going to last you for years to come, the hardest thing you'll have to do from that point on is align that damn y-pipe.