Pack more food, spend more time in the mountains. Not saying you should go faster, but with 7 days of food for the southern section, you can't be spending too much time fishing at Evolution Lake either.
I'll be on or around the JMT this summer between June 30 and August 3. We're a group of 3 with 3 bear canisters for the southern section, 2 canisters in the northern sections (you can mail things out from the Muir Trail Ranch as well, so when we're heading north, one canister goes home by mail from the ranch).
We eat good, and we do a number of day hikes around the trail bagging some peaks. I've hiked th area about 10 times now, and if there's one rule of thumb, especially in the southern half of the trail it is that having enough food is the key to a fun trip.
Since the advent of bear canister requirements, the southern half of the trail has become logistically more difficult (more weight due to canister, less food fits inside unless you carry another one, which in turn is even more weight). Without resupply for over 108 miles you really have to stick to your plan, which is driven by how much food you can pack and how much you are going to eat.
Resupply by horse packers is extremely expensive and almost impossible to do, since they cannot leave the food behind in the backcountry. Timing this is very difficult, unless you hike like clockwork. $500 for such a supply isn't worth it anyway.
Weather can be a factor - it cost us about 2 days last year - allegedly a "once in 5 year monsoonal event" - but hey, we ran right into it and as a result we were running low on food by the time we got across Mather, and that was the end of our hike: we had to exit at Taboose Pass, or we would have been out of food well before Whitney.
Re canister size - I have a Bearvault 500 and a Bearicade Expedition. The Expedition fits about 2 extra days of food over the BV500, while it weighs just little less. I was able to fit 5 days of food for 3 people (one adult, two 10-year-olds) into the Bearikade Expedition last summer, so you should easily fit 7-8 days into the Bearvault for one person.
Stay away from freeze dried Mountain House-like stuff - very bulky compared to packing your own pasta or minute rice meals that cook in just minutes. Gas cartriges don't have to fit into the bear canister, and in some select areas you can even cook on a wood fire. I think if you cook with kerosene, you must fit that into the canister just like all other things that smell.