I wouldn't really make any blanket statements about the Sidewinder intake....it actually does quite well.
Lykins Motorsports 427FE Build, Alan Carter
I do quite a few standard stroke 427 builds, some with aftermarket heads, some with factory heads.
Alan's 427 made 526 hp @ 6200 with 511 lb-ft of torque, with ported MR heads, a Sidewinder intake, and a small-ish hydraulic roller.
I did a 427 with some Pond heads a while back, a solid flat tappet, and a Performer RPM....it also made 525 hp.
The 480 hp estimate for the engine in the link is pretty close, if not a little optimistic. 428CJ heads, in stock form, flow about 240-250 cfm and will make about 425 hp on a 428 with a hydraulic roller and a factory CJ intake.