8MHz should work at this data-rate, but take into account that the iinternal osc can/will drift - so and it's not the best option for timing sensitve things like serial data exchange. A crystal is by far the best option if you want repeatable results under varying conditions.

Temperature changes will cause internal oscillator frequency drift & loss of communications/data. You have the option of tuning the internal osc to compensate for freq drift, but it's more of a pain than it's worth in my opinion.