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The real world difference in speed between a 1.1 ghz macbook and 1.3 ghz macbook will be negligible.

They both turbo, and both will hit thermal throttling if turboing for extended periods. The max speed difference between the base 1.1 and 1.3 top of the line is under 20% - and that's when running entirely CPU bound tasks.

If any of the macbook CPUs is too slow for what you're doing, you need to step to a different model machine really to get any significant difference in performance.
 
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