I'm sure the OP knows how far things are.
That said, if going from Ft. Walton Beach to say Santa Barbara, I'd use I-10 (not I-40).
The Wine Country in Santa Barbara is kind of neat. Then go up the coast toward Napa Valley, etc.
Even if you skip Santa Barbara & go to Napa. Google maps has via I-10: 2,512 mi, 36 hours.
Via I-20 to Dallas to I-40: 2,440 mi, 37 hours.
Via I-20 W & I-10: 2,530 mi, 37 hours.
Except for I-10, one would have to cut up to reach I-20 from FL.
With leaving in Oct, I-10 route would be warmer:
Old Post On Much of the Area TX, NM, AZ. Not all along I-10, some I-20 & I-40.
Maybe some new in this one
I-10 In AZ & Carlsbad, NM?
More Misc.
Texas & New Mexico links.
Link for California:
In Los Angles Area One would take US 101 to go north to Santa Barbara & Napa. I'd use the 210 freeway from I-10 in San Bernardino which will change into the 101 by keeping on the 210 (around Pasadena one has to get off the 210 to stay on the 210; by just staying put, not turning off, it'll soon be the 101 with another number change in between). Not too difficult of a drive when not in rush hour traffic....good to go between 9 am & 3:30/4 pm. Normally.
If wanting to bypass Santa Barbara, take the turn to get back on the 210 in Pasadena, take 210 to the I-5 N. But this is an inland route, where as the 101 does follow the coast for much of the way or is nearer the coast, to be able to cut over to it. CA 1 is a neat drive, but can have lots of curves & some hills. Not too bad from Monterey to Half Moon Bay.
Texas Hill County Vineyards ---
Texas Wine New Mexico Vinyards --
Ditto But by Region One in Deming just off I-10. The 81 Palms (55 RV Park) is next to Luna Rossa Winery in Deming.
http://www.lunarossawinery.com/Some in Las Cruces as well.
Cruces Wineries ---
http://www.lunarossawinery.com/contact Arizona Vineyards There is at least one in Wilcox.
AZ Wine CA Vineyards --
Santa Barbara Wine Country ---
Map CA Wine CountryI have done I-20 from back east (years ago) to New Mexico. It wasn't too bad a route back then. Only done I-10 in LA from somewhere east of Lake Charles (long ago). It was somewhat rough getting to Lake Charles in some places back then (had a long stretch of bridges & causeways getting across a bayou or bayous I remember with not much if any sides to pull over if needing to).
We use I-10 from Cruces to Tucson every other month or so. Not a bad drive. Over the years we have used I-10 to Los Angles Area hundreds of time. Not bad at all.
Have used I-40 a few times, seems to be a little more truck traffic at times, more hills to scale (nothing too major, but more than I-10). Higher Elevations along it.
Must repeat this: If you haven't gone to see "Hearst Castle". "Hearst San Simeon State Historical Monument" is a must see. And San Simeon State Park is just south of the Monument.
The Monterey Bay Aquarium in Monterey is really great. North of Monterey at Moss Landing is a great sea food place over by the docks, called Phil's Fish Market & Eatery.
Monterey Wine TastingI have driven to Columbus from New Mexico (late 90s) using I-40 to OK City, I-44 to St Louis, 1-70 to Columbus. Drove back the same way. My daughter did an internship some summer at the Hyatt Regency. I helped drive her out, then drive back at end of the summer. I-40 would be following the old Route 66 route. An easy drive.
Happy Travels!