Assuming you're talking about a current-generation Macbook or Macbook Pro, the difference in performance between the two models you cited (2.3 GHz w/ 6 MB L3 cache vs. 2.7 GHz w/ 8 MB L3 cache) will make, roughly, between a 2% to 15% difference, depending on the exact workload. It's definitely nothing earth-shattering. But it all depends on how long it takes for your data to calculate. My figure of 2% to 15% comes from what I have read in reviews and benchmarks of modern (Ivy Bridge and Haswell) laptop-scale processors, of the same generation, with different clock rates. Generally, the single-threaded performance difference between the slowest one and the fastest one is around 25% in extremely specific synthetic benchmarks; 10-15% in average cases; and 2% or less in some benchmarks that really don't come close to taxing the single-thread performance at all (or exhibit bottlenecks elsewhere in the system, e.g. I/O).
To use a ridiculous example, if it took 1 million years for your numpy array computations to come through on the 2.3 GHz processor, shaving off 15% would save you 150,000 years -- or about as long as homo sapiens sapiens has been mucking around.
Obviously, if you had a lifespan of, say, 2 million years, shaving off 150k would make a huge difference. You might even be able to run the calculation twice before you land on your death bed.
On the other hand, if your calculations run nearly instantaneously on most modern CPUs, adding 15% performance won't matter much at all. Take for example something like running Google Chrome. Will you notice any perceptible difference at all in the speed at which webpages and videos load, while running a current-gen Macbook with those two different processors? I severely doubt you would be able to perceive the difference at all. But then if you started loading a 24 GB HTML file that took several hours to parse, the difference might start to stack up into measurable time.
In the end, you're either going to sacrifice time, or sacrifice money, when you're doing stuff involving computationally-intensive algorithms that take more than a few milliseconds to complete. If you get the slow processor, you'll wait longer as a consequence of paying less money. If you get the fast processor, you'll pay more as a consequence of not having to wait as long.
As it stands, this is essentially a purchase recommendation. However If you would generalise the question somewhat - perhaps asking about the advantages of more l3 cache for example, this might end up being more useful to a wider audience. – Journeyman Geek – 2014-09-25T01:29:52.820