First, on this comparison, it's clear Shimano is uncompetitive. SRAM comes out the best, with Campy a close second.
But second, sticking with complete groups, the jump to the highest end comes with a hefty price tag. Each is over $5/gram. Among the second-tier groups, Force shows itself as the real weight-weenie bargain. With performance essentially equivalent to Red (with exception of the ceramic bearings, which might be important), it sacrifices less than 150 grams.
And it's easy to make up that weight for less money than the Red upgrade. For example, I show how swapping the Force crankset for a Vumaquad comes out lighter than Red at less money, even though the Vumaquad is a boutique-level crankset. The Lightning crankset could yield the same mass as the VumaQuad at around $350 less. However, I was sticking with parts Competitive Cyclist sells. In any case, the Lightning gives up some stiffness to the SRAM cranksets, and while crank stiffness isn't a big deal for my power and mass, the stiffer Vumaquad makes my point better.