One thing Ive bever known for sure is at what depth generally when to switch to a deep diving jerkbait. 

Going to fish for smallies tmrw in a deep rocky reservoir, with nothing but steep slopes and one flat.  Water visibility should be 4-6ft. Would a x-80 trick darter (4-8ft) on 6lb line allow it to get deep enough to effectly fish ledges that get deep quickIy? Water temps are probably 45-55 degrees.

Thanks for any advice guys.

That would depend on a number of things, the most important being; Where are they and how deep are they?  If they're holding or suspending at 10-12ft. it would be an option, but if they're at 20+ft. I think you know the answer.