I drive Fresno to Lone Pine, and sometimes take the route from Bakersfield through Isabella, and other times Bakersfield through Tehachapi.
Google reports the Tehachapi route to be 13 miles farther and 3 minutes longer. But for ease of driving, the Tehachapi route is much better. The Isabella route has some terribly winding sections, and all the rest is two lane. If you get behind a line of cars, you're stuck. However, the Isabella route is prettier, so if you are traveling during the day, it is worth considering.
It has been a number of years since I took the 155 out of Isabella, and it seemed to go on forever! The endless slow curves was mind-numbing. It was one of those "never again" experiences.
That stretch of one-lane between Three Rivers to Mineral King will probably be all the slow road you can stand. Google shows "27.6 mi, 1 hour 4 mins Mineral King Rd"
If I were driving, I'd go Visalia, Bakersfield, Tehachapi.
And best of luck on the hike! What route out of Mineral King are you taking? It should be fun seeing Whitney from the pass, before getting there 2-3 days later.
And we definitely want a report, both of the hike, AND your driving route.