I believe that both are very challenging deliverables and it'll take a good leader to do one let alone both.
If you look at our past, Kenya has had two leaders who delivered somewhat on (a), but because they didn't deliver sustainable growth, their record is somewhat tarnished. Up until mid70s, Kenyatta had allowed Kenya's economy to grow at a good speed. Corruption and signification changes such as allowing civil servants to own businesses; rampant tribalism meant that there was anxiety as he approached his last days and political assassinations meant he bequeathed a failing template.
Hopefully we can't argue that Kibaki has implemented policies that have allowed the economy to grow during his term so far. And yet, the anxiety we collectively feel about 2012, says a lot about his failure to deliver a sustainable growth model...
A sustainable growth model is difficult to deliver because it requires the deliverer to be of sustainable habits. If you are corrupt, tribal, uneducated, don't do politics, vision-challenged and so forth, you won't deliver a good legacy. You won't build institutions that are sustainable. Your going will find people rushing in to replicate your habits.
The search continues...