we did the trip the opposite way last year.
estepona to roda.
we went the coast rd which took about 5 hrs but there was a section with road works and you do have to go through some towns where going was slow.
its def quicker going the granada way and i would do that if i was going again.
we went down to gibralta from estepona for the day which was an easy 1.5 hrs and well worth it.
if you go there then instead of turning right to drive into gib turn left and park in the undergroud parking opposite the border.
walk through customs and accross the runway and grab a taxi to do the rock tour - its well worth it and it drops you off down in the main st after.