If you look here: http://homepage.ntlworld.com/davidtoms you can see our pictures of what Fuller ridge, Baden powell and the Sierra looked like this year with an April 10th start and a June 1st departure from KM. Unless 2006 is another 1 in 10 high snow year, its unlikely to be worse than this on June 1st, and you can form your own opinion of whether these conditions look like the kind of experience you want. Squeaky’s journal on trailjournals shows pictures of the Sierra with a May 23rd entry.
Early April in soCal was pretty cold this year - just below freezing at night for the first 1-200 miles even in the ‘desert’.
Re bags - we had no problems using down bags with only 8oz of fill each, although the bags were custom cut for us, had no zips, and were very warm for the 1lb weight. There’s no direct US equivalent that I’m aware of - the WM ultralight has more down, and the highlight has a similar amount of down but also a part zip and some strange baffling. We used a stephenson tent which is much warmer than a tarp or a normal tent and gave us a few degrees extra. We also wore all our clothes on the coldest nights, but were never cold.
An alternative to a warmer bag would be to carry a WM flight jacket (as we did) for the sierras, and sleep in that if you’re cold. Has the advantage you can wear it around camp as well.
We hiked a pretty average pace (150-170 miles a week) and finished Sept 9th. The snow probably slowed us down by about a week, i.e. if the only snow had been above 10,500ft from KM onwards, we’d have finished at the start of September.
The nice thing with starting early is how incredibly peaceful and empty the trail is. If you’re solo you may not want this.
Dave