I no longer worry about the heat from overclocking. Outside in the sun the temp gets up to 120 or 140F (in which case it runs at stock speed), whereas indoors with overclocking I've not noticed anything above 112F.
You may not worry about it; Motorola has to. Heat is the enemy of all electronic components. A chip's speed rating is calculated in large part on the basis of the percentage of units that will fail at a particular clock speed. A small percentage will fail running at the stock speed; a larger percentage at 10% above the stock speed; a still larger percentage at 20% above, etc.
The manufacturer determines a stock clock speed based on the tradeoff between performance and failure rates.
Your particular cpu may run fine at 800 mghz or even 1.2 gighz. And it may never fail. On the other hand, it will probably run fine until it's fried. You may not care and assume you can always get a replacement after your cpu melts. Of course, if that occurs you won't be in a position to put your phone "back to stock." And if your insurer determines you've modified the phone, it won't be covered by insurance.