Playing the devil's advocate:
This costs $13,781 for 620hp which is $22.22 per hp.
This on the other hand is $20k for $638hp which works out to be $31.35 pr hp. I can't begin to guess where the ratio goes at 950hp.
I realize there is more usable power under the curve on the LS AND it will get more mpg then the 572 but I also believe the cost to install the LS motor has significant adders over what it takes to install the 572 in a popular muscle car. I'm willing to bet that the install delta between these two options if not performing the swap yourself is close to 10K. If you are a diy- it is harder to speculate on a theoretical skill set and the value offset.
So one gets 10mpg and the other gets 18mpg while costing $10-20k more. How long till you make up that delta?
Taking the cost out and factoring only weight, performance, reliability type things- the LS certainly make a lot of sense. I do understand their appeal.