The only way you can accurately compare a Carrera intake to a stock 930 intake is by doing an EFI conversion using a stock 930 intake - both on the same engine. I have never seen that done on the same engine.
What you choose depends greatly on what your goals and budget are. Carrera manifolds go for around $250-500 depending upon condition and EFI equipment.
The 930 manifold will support 500HP so it isn't a horrific piece.
The Carrera manifold might better lend itself to a 400+HP application where head work is going to be done (you must do something to address the difference in port size from stock 930 heads and stock Carrera manifold).
The Carrera intake makes an EFI conversion easier if you plan to use the Motronic system of the 3.2L engine.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8