Can someone explain me why the Ati X1800XT Master Cards are clocked to 600MHz core and the Ati X1800XT are clocked to 625MHz core???And same with the memory 1400/1500

i am a little confused....

ATI X1800XT Master Card specs:

- Powered by ATI Radeon R520XT GPU running at 600MHz
- Based on 0.09 micron manufacturing process
- 16 ultra efficient extreme pipelines
- 256MB GDDR3 Memory running at 1400MHz
- 256-Bit lightning fast memory interface
- 8 Vertex Shaders/Geometry Pipelines
- Memory Bandwidth - 45GB/sec
- Fill Rate - 9.80 billion pixels/sec
- Vertex and Pixel Shader Version 3.0
- 10-bit Native Display Quality for future LCD technology
- ATI® Crossfire™ Ready (Slave card required)
- 3Dc+ Technology
- AVIVO Technology - H.264 Support
- Microsoft® DirectX® 9.0c Shader Model 3.0 support
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ΑTI X1800XT crossfire ready/master required

- Powered by ATI Radeon R520XT GPU running at 625MHz
- Based on 0.09 micron manufacturing process
- 16 ultra efficient extreme pipelines
- 512MB GDDR3 Memory running at 1500MHz
- 256-Bit lightning fast memory interface (512-bit Ringbus)
- 8 Vertex Shaders/Geometry Pipelines
- Memory Bandwidth - 48GB/sec
- Fill Rate - 10.00 billion pixels/sec
- Vertex and Pixel Shader Version 3.0
- 10-bit Native Display Quality for future LCD technology
- ATI® Crossfire™ Ready (Crossfire/Master Edition card required)
- 3Dc+ Technology
- AVIVO Technology - H.264 Support
- Microsoft® DirectX® 9.0c Shader Model 3.0 support