Casting a tip is easier for me, more weight at the head and it shoots much nicer. Is there any difference in presentation when comparing a sink tip and a full sink line?
Yes - what Ralph said. I learned that lesson the hard way back in 1999 while fishing for pinks. I was using a full sinking line (normally used for trout lakes) and my presentation just got swept out of the zone. Meanwhile, my fishing "mentor" was into fish after fish using a sinking tip system (we were using the same flies). The ability to mend line is critical for a drag free drift in flowing water.
Anyway, later in the 1999 season, I switched up to a full floating line with long leaders and split shot to get into the zone. It worked as far as hooking fish, but was terrible to cast! I ended up investing in the proper gear and with a sinking tip system, my success rate for salmon and steelhead went way up.
However, for Stillwater a full sinking line is far better than a sink tip line IMHO. In fact, I've got a Loop Evotec trout reel loaded up with a 5 wt Rio versitip system that has never been used! I'm thinking this would be a great set up for trout in flowing water. However, for stillwaters I haven't had a need for it yet.