The 4.8 will be strong and make the power with enough boost. A larger motor will be more powerful at part throttle, which is where a street motor spends more time. Both can have strong power curves, but the smaller engine will be putting a lot more boost through to get it. It will also cost a lot less.

Take the advice about smaller bores. Big bores are great on RHS or Dart blocks etc made for it, but on an LS3 or LS7 block I'd be keeping bores stock and use more boost to get that extra kick. Darton sleeves are still a good idea along with studs top and bottom, but again OEM blocks are going to be up there trying to run mid 8's at 3800lb so thicker walls are better.

As for lag - don't worry about it - you have an auto. Unless you are trying to run twin big thumpers or old tech turbos - the car will spin up fast enough, especially with a converter. If you ran a manual - different answer and yes, turbo sizing is more critical. Even a remote rear mount can spool from a dig with an auto