IMO, there is no tangible difference between the d15b and d16z6 in terms of performance potential, or just about anything else for that matter. You'd be "different" in tems of engine-code (for what thats worth), but not for any other reason. The fact that nobody builds up their d15b is more atributable to the relative rarity of the motor itself than the performance potential of that motor, or any other.
That said, since you're getting the motor anyway, do what you want with it. If you want a built and heavily boosted d15b, go for it. More power to you. I would like to see what you could do with it.
