Mike,
I've been up Whitney several times via the Main Trail and the Mountaineer's Route. I have summited two of the Pallisades' fourteeners, Thunderbolt and Split. I am a part of a group that will be attempting the remaining five peaks this August (North Pal, Starlight, Polemonium, Sill, and Middle Pal). Next week I'm planning to summit Mt Russell, Whitney & Muir as a warm up for our trip to the Pallisades next month.
I suggest that Mt. Sill should not be considered a "warm-up" for Whitney. The Pallisades are in a an all together different league compared to the Whitney Trail. A scramble up to Sill may be one of the less technical Pallisade fourteeners, but one should be prepared for, glacier travel, third, fourth, or even fifth class climbing depending on which route is selected.
If your primary objective is to see the Palisade Glacier, the North Fork Big Pine Creek Trail will get you there without requiring too much technical mountaineering preparation. If you are considering travel up the glacier, keep in mind that with the low snow fall last winter, higher than usual temperatures, and an early melt, the glacier is not displaying the most human-friendly conditions this summer. Recent reports indicate that the glacier is 4 to 6 weeks ahead of the typical seasonal melt cycle. This includes exposed solid ice, waist deep sun-cups, open crevases, and possibly an un-crossable bergschrund at the transition from ice to rock.
I would recommend doing some home-work by checking out available information in Secor's "Peaks, Passes & Trails", in Cameron/Burns' "California Fourteeners", and SummitPost.org.
Enjoy the mountains safely,
-Rick F.