You know, I heard about these bad boys just the other day and am in contact with Garrett to get more info.
Nix: the key is whether or not they are also more efficient. Higher efficiency translates into more horsepower and horsepower is good.
While it's true that you are still limited to the capability of the stock engine, having these installed from the get go and building the motor down the road ultimately gives you more headroom for additional power.
Again, we're looking into whether or not these can be used without redesigning the whole kit. I'll post back with updates as I get them.