Ditto with Buddy. That deep requires full sinking, not just a sink-tip. Right now at Henry's Lake here in Idaho the fish have moved into the shallower water (2-6 ft.) along the lake margins, so an intermediate (1.5 to 2 ips sink rate) line is called for. During the early season the fish are hugging the bottom so a full sinking line is not only desired but manditory.
I use a Class VI Sink-tip for my river fishing and never for the lake. I use full sinking as Buddy described and Intermediate lines for the lakes depending on whether I'm fishing the depths or the margins.

Kelly