As people have pointed out, the 2600 is underclocked. But please don't just think it is a heat issue. Heat comes into it of course, the designers are more concerned with reliability.
As a Design Manager for a well known consumer electronics company, I can tell you this: Typically we are given a spec. telling us what the product life time should, 2 years 5 years or sometimes 10 years, all quoted in hours. On this basis we make our first engineering samples to conduct design validation trials, for such things as component open and short circuit tests, as there are many safety directives in many countries that dictate how a product should fail and fail safely in the event of a fault. We conduct EMC trials and most importantly deration/performance tests. The unit is loaded as it would be in normal use and measurements are taken at high, low and average line voltages. So for a 1 watt resistor for example, we would never run it at more tan 50% of its capability, as anything more could shorten its life, this applies to all components, we use a 70% limit for semiconductors and 50% pretty much for everything else. We also take into account the ambient temperatures that it may see, +50 deg.C and say -10 Deg.C. With all this data we use a nice little piece of reliability software that calculates the expected life of the product. If it spits out a figure that is too high, we can take cost out and vice versa. The biggest weakness in most electronics is the electrolytic capacitors, they have to be kept cool or their life expectation drops rapidly. So that is just a small insight into electronics design.
So in a nut shell, they don't like hot stuff in the cases as product fails and is returned, they lose money and reputation. If you ever wonder why some Panasonic, Sony or other reputable brands sometimes cost more, it is because the spec says 80,000hrs or 100,000 hrs MTBF.
You could off course overclock it, add big heatsinks and fans, cut a hole in the case to get the air volume and parts in, but it would not look nice and your warranty is up the creek..LoL