The difficulty of any climb will depend on its length, steepness, wind speed and wind direction, the total weight of you and your bike, and, of course, your fitness and your intended speed.
Stephen Touset has thoughtfully provided a link that shows the elevation profile for the climb. The grade appears to be relatively even rather than a series of steeper and flatter "stair steps" so with a few other assumptions we can put some bounds on how much power you would need to produce to climb from Marbella to Ojen at different speeds.
The power equation has four main parts as was described in this bicycles.stackexchange post: a part that describes the power needed to overcome rolling resistance, a part describing the power needed to overcome changes in elevation (potential energy), a part describing the power needed to overcome changes in speed (kinetic energy), a part describing the power needed to overcome aerodynamic drag. When climbing a hill, of course, the potential energy component dominates.
Using assumptions about rolling resistance, aerodynamic drag area, air density, and weight that are in the "normal" range, we can therefore make a ballpark estimate the total power needed. The estimate won't be exact but it should give you an idea of the power required. Further, I have divided total power by an estimated body weight to get "watts/kg" which is a standard way to describe an athlete's power production. Tour de France riders can maintain 6.0 watts/kg for a considerable length of time, a domestic pro racer may average 5.0 watts/kg, a very fit recreational racer may average 4 watts/kg, and a commuter riding home after a long day's work might be able to maintain 1.5 - 2.0 watts/kg. Finally, I have converted speed into the number of minutes needed to travel 5.9 miles while climbing a steady 4.8% slope. The plot below summarizes this information, with the x-axis showing the number of minutes and the y-axis showing the output in watts standardized by body mass in kg. If you can average 4 watts/kg, it will take around 25 minutes for the climb. If you average 1.5 watts/kg, it will take about an hour.
As an aside, this bicycles stackexchange post shows examples of Category 2 climbs from recent Tours de France.
Here, for example, is are the categorized climbs from the 2012 Tour. At 5.9 miles (9.5 km) and 4.8%, the Marbella-Ojen climb would evidently fit right into category 2.