So, any lower speed is good enough for simple apps.
Timing using simple delay loop is acceptable for testing.

From your post I guess you are a newbie, hence the lecture below:
There are some pitfalls in such delay loops:
If your app is complex, then you are wasting CPU clock cycles in idling.
If your code is in C and you switch on the code optimizations, the delay value will decrease,
that is the freq will go up and if that exceeds 100k, then you will get erratic behaviour in EEPROM comms.
So, don't be tempted to enable the code optimizer of your C compiler.
And most important, don't forget to see some excellent sample code on this website,
link on the left "Code Library".