Mazatlan

We too, love Mazatlan. We actually spent a couple of winters there.
IF you stay in the area of the Gold Zone, take the bypass until you hit the first exit, labeled appropriately, Zona Dorada. It takes you past the new shopping center, complete with a Sears, and you end up at the marina, between the two bridges. It was so nice to avoid the major part of town.
Like you, we have the 500, 400, 300, 200 formula. That's approximately, in miles. From Mazatlan, we go to San Carlos, from there, Ajo, Arizona, because it's an easy border crossing, saves us miles, and is a nice road. To Palm Springs, where we are tonight, then home.
We will be home tomorrow, first time back on our beach since October 17. Yes, we are looking forward to our yard, garden and beach, but not the cold water. Fortunately, it will be 72F tomorrow, but 50 at night. Maybe someday we will be able to move to Zihua permanently. Because we work on line, we started working last week, so the vaca is definitely over!
Safe travels to you, too.

Do you cross at Sonoyta/Lukeville? No problems getting your vehicle deposit back at that crossing?
Heading north from San Carlos, where do you swing over to the west? Been to Bahia Kino? Is it worth a sidetrip, assuming we eventually cross at Nogales?
Re Mazatlan: we enjoy it for 3 or 4 days on the way south, then again on the way home. But for a long-stay, it can't compare to Zihua.