frame geometry question

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I have an '05 Specialized FSR XC. The rear travel is specified at 100mm. The stock front fork (a so, so Manitou Axel Comp) is also 100mm. If I wanted to upgrade to a Fox Float 130 XTT or some such larger travel fork (but probably not over 140mm) should I look to upgrade the rear shock to increase that 100mm of rear travel? The geometry of the bike is such that the FSR suspension actually will travel more than 100mm....I can hike the bike up higher in theory. I've been told by a couple of experienced full sus. riders that you should always keep the geometry the same..meaning..keep the travel the same front and rear. Makes sense. So my question is specific to this particular bike. Would increasing the rear travel with a longer shock cause undue stress on the rear suspension unit if i need to match the front travel?

Any insight is more than welcome.