I need to do away with my old intake setup when I change to a top mount turbo setup and I'm wondering what size to go with for the inlet piping to the turbo.  Is there a point where a larger diameter doesn't give any return as it needs to step down the inlet size before hitting the compressor wheel anyway?
 
The turbo will be flowing 550-600lb/hr if I push it to the limit and the turbo inlet is 2.5 inches. I will be using a cone filter setup onto an aluminium velocity stack which will then transition to the piping, this is the setup I am currently running and I love the way it amplifies all the turbo intake noise :)
 
The choices I have are a velocity stack with 6 inch outer diameter transitioning to 3 inch, 3 1/2 inch or 4 inch piping.
 
So should I apply the bigger is better approach that people go for when sizing the exhaust system for a turbo or stick with something closer to the inlet size?