the better the system flows (intake piping, porting, ect) the less psi your turbos will be generating in your manifold at any given power level. I know you had to replace the actuators with the original GT2560R (GT28R) writeup (for obtaining them directly from Garrett or a reseller), but when you buy the 600R kit from Z1 it already has everything you need including correct adjustable actuators as seen in this picture ripped from their product page.
Rule of thumb is 555 injectors are probably good up to about ~500RWHP I personally wouldn't push them much further and it will be tough to get the GT2560R (same turbo as the 600R kit) to make too much more than than without plenty more mods, so you might be OK. If you plan to go over 500RWHP you will want 740 or 850 injectors and IMO you would also want bigger turbos like the GT2860R kit from Z1 (675 kit) or JWT (700bb) but I would swap the exhaust housing on the JWT kit as I recommended below.
m a g l i t o Original engine destroyed itself...new engine being built now. Full official details coming soon. sig photo by me effects by ZXRider(SoCal) The build up begins - progress - reassembly part one - part two
Too many variables to say - 
