Hi kaiowolf,
as already said, you will not have any performance issues playing your games from a modern USB 3.0 external drive as long as you make sure you are using a newer drive series.
Additionally, our own and independent research on current hard drive series do not show significant differences in drive reliability. Nowadays objectively all major hard drive manufacturers are working hard to optimize performance as well as reliability with each new generation of drives. If the right drive type is used in each scenario, modern hard drives usually last much longer than their minimum life time expectancy.
Therefore, RPM is not necessarily the only factor you should take into account. In regards to performance and lifetime...