I'm coming up with a pros/cons of each option and having a hard time finding facts on the 4G63 weight.
The first hit on a Google search for the LS4 came up with this:
478lb engine (dry) and 214lb tranny.
(GM LS4 V8 / 4T65E INFO)
That appears to be anywhere from 200-300lb heavier, so if one wanted to keep a similar P/W ratio, it'd need more horsies to boot.
I'll share my pros and cons once I've figured them out.
I browsed the dsmtuners forums and found that the long block is right at about 300-320 pounds. Adding all of the sensors, manifolds, turbo pieces puts the engine in the neighborhood of 420-480 pounds. The transmission is about 150 pounds. These are all dry weights.