Steady, consistent 25-35 mph winds daily in December in La Ventana, Mexico! Big swells roll across the Sea of Cortez with surf crashing on the shores. I've always sailed the flat windy waters of the Pamlico Sound in Cape Hatteras every April since 2000, so it was somewhat challenging to get used to plowing 
through the shore break to launch. Be ready for deep water starts if you miss your jibes on the open sea. No problem...someone from Ventana Windsports will come get you downwind with the ATV so you don't have to do the schlepp of shame back. You get the ride of shame instead ;) I've never seen more kiteboarders - more than windsurfers.
We stayed at Ventana Windsports with really nice private cabanas and three wonderful meals served daily. Windsurf equipment rentals are available offering the latest equipment from beginner to advanced. 
The winds are usually calm in the morning, but you can see the wind line rush across the water and arrives like clockwork every day at 11:00am. The wind blows consistently for the rest of the day and often through the night. The cycle repeated every day we were there. I usually sailed a 4.7M sail in the morning and 4.2M in the afternoon. I used a 95L board, but probably needed something in the low 80s. My only concern was not being able to waterstart on a smaller board way out over my head with the big rollers crashing over my head.
The strong winds made it a little chilly during the day, but if you find a non-windy sunny spot, you can get a good tan.
It was dangerous driving at night (and even during the day) due to the bull cows roaming freely throughout the countryside. There are no street lights on the dirt road you take if you fly into Cabo making it an adventurous and exciting ride.
We took a 30-minute ride in the car north one day to the beautiful seaside town of La Paz. It reminded me of the promenade in Cannes, France in the French Riveria. I would return to the Baja again in a heartbeat - maybe in February when it's a little warmer.