Getting from TJ to Guerrero Negro on the first day and all the way to Cabo the second day sounds like torture to me. Some areas are quite slow going. Why the rush? If you're just interested in getting to Cabo how about flying?

We've done both (driven and flown). In February we flew to Cabo and rented a car for something crazy like $100 a week! Spent 5 days getting up to Bahia Magdalena (Puerto Lopez Mateos) to see the whales. I like the southern half of Baja much more than the northern half. Given how cheap rental cars and flights are (or can be depending on when you're going) we probably won't do the full drive again. The north just isn't that nice and it's a bit dangerous these days.

The time we drove down my husband had cell coverage pretty much the whole way but he has a GSM phone.

Consider using the Tecate border crossing at least one way. Easier to cross here and the road goes through some attractive country.