You could indeed use the EVO charger for the Kindle 2. The difference between 4.9 and 5.0V is negligible, considering the fact that the emf of either charger will likely vary by more than .1V. And the Kindle will only draw .85A from the quoted 1.0A PS of the EVO, so there's no problem there...
Don't use a higher voltage than is recommended, you may charge faster, but it will be terrible for the components. You can't push a higher current through the phone than it is meant to take, either. In other words, just use the stock charger.