The most accurate specs I have found are fairly common across the internet, save for sites favoring Xbox or PS2 which tend to use outdated specs or twising them around a bit.  Nintendo went real conservative and realistic whereas the other guys listed figures that you never come close to in a real game.  Gamecube even had at least one launch title that blew past the listed polygon performance, not to mention some of the games that followed, while no PS2 or Xbox game has yet came close to reaching figures listed in their specs.  They won't ever push 120 million polygons a second, 80 million, 60, or even 40 million polygons per second.  Heck PS2 launch titles averaged 1 to 3 million.
The best I can give is this:
MPU("Microprocessor Unit")* = Custom IBM Power PC "Gekko" 
  
 Manufacturing Process =  0.18 micron IBM Copper Wire Technology 
  
 Clock Frequency = 485 MHz 
  
 CPU Capacity = 1125 Dmips (Dhrystone 2.1) 
  
 Internal Data Precision = 32-bit Integer & 64-bit Floating-point 
  
 External Bus = 1.3GB/second peak bandwidth (32-bit address space, 64-bit data bus 162 MHz clock) 
  
 Internal Cache = L1: Instruction 32KB, Data 32KB (8 way) L2: 256KB (2 way) 
  
 System LSI = Custom ATI/Nintendo "Flipper" 
  
 Manufacturing Process = 0.18 micron NEC Embedded DRAM Process 
  
 Clock Frequency = 162 MHz 
  
 Embedded Frame Buffer = Approx. 2MB Sustainable Latency : 6.2ns (1T-SRAM) 
  
 Embedded Texture Cache =  Approx. 1MB Sustainable Latency : 6.2ns (1T-SRAM) 
  
 Texture Read Bandwidth =  10.4GB/second (Peak) 
  
 Main Memory Bandwidth = 2.6GB/second (Peak) 
  
 Pixel Depth = 24-bit Color, 24-bit Z Buffer 
  
 Image Processing Functions = Fog, Subpixel Anti-aliasing, 8 Hardware Lights, Alpha Blending, Virtual Texture Design, Multi-texturing, Bump Mapping, Environment Mapping, MIP Mapping, Bilinear Filtering, Trilinear Filtering, Anisotropic Filtering, Real-time Hardware Texture Decompression (S3TC), Real-time Decompression of Display List, HW 3-line Deflickering filter  
  
 
 
 Sound Processor = custom Macronix 16-bit DSP 
  
 Instruction Memory = 8KB RAM + 8KB ROM 
  
 Data Memory = 8KB RAM + 4KB ROM 
  
 Clock Frequency =  81 MHz 
  
 Performance = 64 simultaneous channels, ADPCM encoding 
  
 Sampling Frequency = 48KHz 
  
 System Floating-point Arithmetic Capability = 10.5 GFLOPS (Peak) (MPU, Geometry Engine, HW Lighting Total) 
  
 Real-world polygon = 6 million to 12 million polygons/second (Peak) (Assuming actual game conditions with complex models, fully textured, fully lit, etc.) 
  
 System Memory = 40MB 
  
 Main Memory = 24 MB MoSys 1T-SRAM, Approximately 10ns Sustainable Latency 
  
 A-Memory = 16MB (81MHz DRAM)  
  
 Disc Drive = CAV (Constant Angular Velocity) System  
  
 Average Access Time = 128ms 
  
 Data Transfer Speed  16Mbps to 25Mbps 
  
 Media = 3 inch NINTENDO GAMECUBE Disc based on Matsushita's
Optical Disc Technology, Approx. 1.5GB Capacity 
  
 Input/Output = Controller Port x4
Memory Card Slot x2
Analog AV Output x1
Digital AV Output x1
High-Speed Serial Port x2
High-speed Parallel Port x1  
  
 Power Supply  AC Adapter DC12V x 3.25A 
  
 Main Unit Dimensions  4.3"(H) x 5.9"(W) x 6.3"(D)