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As Dunk says, the difference is focal length. However, this actually does not mean one has more "power" than the other. While with the same eyepiece will give more magnification in one (the longer focal length), the actual limiting magnification is actually IDENTICAL in each. Barry alludes to what I'm noting below.
The highest practical magnification is determined by the aperture of the scope, not the focal length. The rule of thumb I use is 50X per inch of aperture. So for these two 5" scopes, the highest practical magnification is 250X for both. Exceed the practical limit, and the image begins to degrade and you actually don't gain anything. Magnification is theoretically limitless, but this is not the case.
Now, take a 10" aperture. With the rule of thumb, the highest magnitude is 500X. Again, BUT, there is another limiting factor - the atmosphere. Typical conditions allows only 120X. Good conditions allows 250X. Exceptional conditions and 400X is possible. Go high up in elevation above sea level, and "I've just won Lotto" conditions will allow 800X.
Note, if the instrument you have is of exceptional quality, the 'rule of thumb' upper limit can actually be pushed to 70X per inch of aperture. But, man, this is a rare, rare fish...
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