Unless you equip an older SBC with 15º heads, then the LS1 will kick anything elses ___ GM wise. These cars can be setup to make big power with no real exotic work, plus the firing order is 'better' for those picky about that extra 1% or so from exaust pulsation efficiency/velocity yada yada.
Basically the LS1 is setup almost perfectly right off the bat with what the SBCs only get with machine work and plenty of dough, plus the whole fuel injection thing, carbs make me sick. For an all out race machine thats one thing, but I was making on the (dinosaur) LT1 about 470 HP and getting 17 MPG average, on trips I'd touch into the 20 range, I want to see someone do that with a carb setup. As a joke, "the carbeurator is the only device known to man to provide an innaccurate air/fuel ratio at all RPMs." Better driveability, no fuel float issues in corners, you name it, FI IMO is the sheet.
Port the heads, throw in a cam, and make an easy 500 HP if not more. There are guys doing over 500 RWHP with more work (too bad the internals are so expensive).
Guys making HP like I did with my LT1, are running 10-15º smaller cams, and no headwork are pushing 400 RWHP, passing the sniffer in CA. I am very tempted to get one myself, throw on some LS6 or 6.0L truck heads ported, work the intake possibly (they are not perfect), and someone could find themselves with good driveability, "good" MPG, and 600+ HP depending on your wants, with an under 7k limit if so desired.
All aluminum and 6 bolt mains, FWIW.
For a GM engine it is top dog, no question about it.