The phrase "above that of" is correct and usable in written English.
It is typically used to compare two things or concepts. For example, "The temperatures in June are often above that of March."
All the subsets of CMEs have average speeds above that of the general population.
That percentage is also above that of other companies.
points above that of someone who is mentally retarded.
Brigadier general, military rank just above that of colonel.
Must they yet surface above that of September 11th 2001?
On these experiments, they achieved precision at or above that of the median TREC participant.
Then here we have a third state, over and above that of pleasure and of pain?
The collectivity of the umma elevates the communal interest above that of the individual believer.
The quality, certainly, was a level above that of the afternoon match between Murray and Ferrer.
His low-level job ranks just above that of an intern.
The Democrats' economic record, he asserted, stands far above that of the previous Republican administrations.
