I have been riding in Baja for many years. In March and April, 2003, I made the ride (nearly all off-road and 1,500 miles crisscrossing the peninsula several times) from San Felipe to Cabo San Lucas on my then brand new Yamaha
WR 450F. Once our group left San Felipe, premium gas was often not available. My stock bike, ridden conservatively through every kind of terrain Baja had to offer, ran just fine on both Magna 87 octane and Premium 91 octane fuel. One thing to remember, Mexican gasoline in Baja California does not contain ethanol -- absolutely, positively and recently tested in 2013 by one of the original owners of Maxima
My recommendation to you is to always use 91 octane fuel whenever it is available, however. Use 87 octane if that's all that is available and ride easy. My son wanted to save a few cents per gallon of gas and blew up the motor on his 2004 Yamaha
WR450F, running California formulated (10% ethanol) Regular 87 octane gas exclusively. He rode hard and often could be found at the sand dunes at Glamis, as well as Superstition Mountain -- "penny wise and pound foolish". Older, wiser and poorer, he replaced the 2004 with a new 2008 model WR and fed it Premium gas only.
I currently own a 2008 model WR that only drinks 91 octane Pemex Premium gasoline and loves it. While the gas in Baja has become a little more expensive than gas in S. CA, my overall cost for fuel is actually lower using Mexican gas. This is because I see higher MPG using Mexican non-ethanol blend gas and I don't have the added cost of fuel stabilizer.