When you run a smaller turbo, you have to turn the boost up higher to achieve the same power that you could reach with a lower setting on a larger turbo. This is due to flow characteristcs and heat created compressing the air. A properly matched turbo will make power just as fast as an SC but will make it with less loss and the ability to make a LOT more power up top.
And as far as "just a 4.0" lol, I have been building Hondas the last year or so just taking a break from muscle cars, I have run T67's on 2.2 liters and made more than 500whp on pump gas, a 4.0 can take a serious turbo and still spool it early and make power all the way up top with little to no lag and good longevity with a good timing curve.
2006 Subaru WRX Limited, Leather and loaded.
2004 Ranger Edge 4x4, 4.10 posi, 3 inch BL, 15x10 Eagles, 33x12.50 BFG AT's.
1993 Honda hatchback, 1.9 liter 13:1 compression forged bottom end, ported head, huge cams. 11.83@116