From what I'm seeing online there are actually very few groups who have made it to the Sierras. Yes, the pack is getting close, but they are nowhere 'deep' as in 1000 miles up the trail. Average seems to be around 300-500 miles in.
By doing longer days I figure that I should be able to hit the larger streams and lakes that never go dry, or only do very late in the season. I'm fully prepared to carry 2 1/2 gallons when I need to through most of the southern section.