In T4 you will be able to drive a S366 with stock injectors and a good tune. They are a cheap turbo (~$600 new), and having a T4 mount gives you the ability to a larger turbo if you add more fuel.
T4i I would go with a Holset H2E or QSSB from WOP. Personally, H2E in stock trim would be my choice. You will be able to drive it with the 120cc's of fuel you have available now, and they are OEM on Cummins L10 series engines so they can be had cheap used. They are also a great platform to built off of, as a modified H2E (66mm compressor, 71mm turbine) will flow more air. Joe can chime in more on this, as I understand he's been running a modified H2E for some time now?
Should add you can also modify the QSSB to a GQSSB down the road if you need more air. Similar idea to a modified H2E.