there is a misconception with running the larger rb30 that it will give you more kw, BUT it will give u more nm...thats for sure
another comparo for you:
my rb26 made 700nm torque whereas my rb30 made 930nm of torque, overall power is much harder hitting & tractable, very hard to explain until u actually jump in an rb30 (chalk & cheese in terms of driveability). the new vg38dett in the r35gtr also supported my decision making to increase capacity.
i could have taken the path of running a t51r snail but i wanted a strong street setup with aggressive midrange as well as wanting that standard look to keep the law happy
paul is running a t51r with the larger t62 housing - its a farken donkey of all donkeys turbo!
i'd keep your coilpacks unless there is a benefit of running splitfires which im unaware of.