Back to an invasion of Southern france:
Not to sure how that could have gone...however...fooling the german's as to where the Allies would land would have been tough. In order to make a landing at the scale that Normandy was. If they assembled in Britian the force would have to leave much earlier than a force making a cross channel invasion. This MASSIVE movement would have allerted all forces in france i bet by the time they were halfway to southern france. Thus Rommel would have been brought back. Forces would have been on full alert. Invasions in Normandy would have been even more bloody, and if small would have a tough time surviving.
By the time the invasion forces made it to Southern france it would be obvious that this was the main body and Hitler would have been able to make the correct strategic decisions. Like as to where the panzers should be and wether to hold the pas de cale. In any event...i doubt surprise would have been achieved and the invasion would have been even more costly.
If there was a build up in north africa or southern italy. It would no doubt be noticed so that would be just as negative.