Rob, I'd recommend you drop the Steripen. This is coming from another Steripen user. I did the JMT this past summer, and I did it with AM drops. If you can manage to hike with only enough water to last you to your next water-stop, before treating with a steripen for the recommend 1:30 minutes (or however long it takes, i can;t remember) than surely you can last the additional 20 mins for the AM treatment to be effective. Aquamira is so effective, and pains free, and lightweight(!) I've been contemplated the sale of my Steripen. With AM, you have no risk of battery failure. I actually had a really awesome conversation with some old skool lightweight backpackers from Canada. They brought up the fact that AquaMira has been around in Canada for ages, and the only reason why they don't list it as being effective against certain diseases, and organisms in US is because the United States FDA hasn't approved of it. In Canada, the aqua mira equivalent has been advertised as killing EVERYTHING. I never got sick on my trip, and I only waited 20 mins between treatment and drinking. I took Mike Clellands's tip and premixed my aqua mira in a small bottle in the beginning of the day. This way I didn't have to wait the 5 min waiting time before I dropped it into the unsanitary water. I would simply roll up into a stream or river, scoop, and drop, and 20 mins later I was drinking amazing water. Honestly, drop the steripen, you won't miss it.
I think it's worth having 1/2 - 1 liter of water on you at all times. There's no point in sacrificing safety to save a couple ounces...no one's comparing base weights out there. This past summer, the 7 miles or so before Red's Meadow had very very little water, and what water was available, was extremely skunky/stagnant or mosquito infested to the point where it was worth just trucking on to Red's. Everywhere else on the trail had very ample water, to the point where you could, if you wanted to, get by with just 1/2 a liter between stops.