There are lot of hikes that make for good conditionors. Alot of moderate to easy summer hikes make for a good conditionor in winter due to the longer approach and snow on the ground. I would recommond going up to sahale when avy conditions are good. You'll get good views and a little work out too. Dickerman and pilchuck are nice work out if you do them both in a day. Get a partner and try to due Ruth and Icy in a day.(I haven't done this one but it seems feasible). I guess the point is there are a lot of good hikes to train on. No one has mentioned the cable line on tiger yet, while not a day hike its gains about 2000ft in 1.5 miles its nice to due when you have a lot of other stuff going on that day.
I would also recommond if possible to train with your partners, since you will be roped up together it sucks if there slow.
My opinion on the weight issue is you need to address your strengths and weakness. When your pushing yourself up a slope is it your lungs or legs that slow you down. If its your legs put some weight in a pack and have at it if its your lungs go trail running.