And even at the 300 whp level, there's the 'quality' of the HP to consider, not just the 'quantity'. A small motor with a big turbo is going to be, even with a $$$$ turbo, going to have some lag. And be a bit peaky. And be a bit 'quirky' at producing power - a bit of an on/off switch. I was able to get mine fairly well behaved using electronic boost control tied to throttle position/RPM (in MS) - that helped get some degree of linearity back into the gas pedal.
But a big NA motor? It's just instant-on with that 300 whp. At low rpms - it's got grunt. At any point in time you press the gas, you've got the HP instantly. And peak HP aside, there's the 'area under the curve' - how wide that torque curve is.
I never weighed my car before with the turbo 16V motor in it, so I can't really compare to say how much weight the turbo LS/6-spd manual added. But my best guess would be 'very little. A chunky iron blocked 4 cylinder vs. a modern al lalu small-block V8? it's not a foregone conclusion that the V8 weighs more, or by much. Who knows, it might even weigh less if you don't have a turbo and use some lighter headers in place of the cast iron exhaust manifolds.
And at least when I bought mine - the alu 5.3's were still relatively cheap. Everyone seems to want the relatively rare alu 5.7/6.0 motors. So while the alu 5.3's weren't dirt cheap like the iron blocked truck motors, they were still less than half the price of the bigger displacement alu motors.
