Or is there some kind of patch to enable the Nvidia overclocking tab
in the card proprieties ?

There is no real "patch" that I know of, but there is one great
program called Power strip (http://66.227.107.157/ps.htm) It can
re-tune almost everything. I am pretty sure that it supports your
card, It does many (even my ancient Matrox Mellenium 2) So take a look
and maximize your cards potential

Anthony Brohan