I generally go with my wife to Beaverhouse the end of August.  I have one of those fancy thermometer which measures water temperature every five feet.  Beaverhouse is a large deep lake.  When I checked the temperature, it was 50 degrees at 30 feet.  At 45 feet it was around 42 degrees.  So there really isn't any need to go much deeper that 35 feet as trout will come up to get a lure.  The Rapala tail dancers will go down to 30 feet when they are trolled.  If the water is really deep I have even used 6 ounce weights to get down a little deeper.  Depending on your speed a six ounce weight doesn't go much deeper than 45 feet.  Of course, how deep a lure runs also depends on how much line you have out.  I found that in 50 feet of water a six ounce weight is not getting caught on rocks.  I generally use a flutter spoon with the heavier weights.  For trout water temperature is really important.