Regarding the length of sink tips. Any sink tip being attached to a floating line will have to sink at an angle. Everything else being equal, the shorter tip has to achieve a greater angle to reach the same depth as the longer tip. Are you with me so far? Were we fishing still water, a sink tip might eventually obtain a 90° angle, hanging straight down. Never going to happen in moving water. So, for the sake of argument, let's assume the maximum angle any sink tip will be able to obtain is 30° The Sin value of 30°=.5 That means maximum depth for a 10 foot sink tip will be 5ft where as a 15ft sink tip will get down to 7.5 ft. This is all theoretical of course, it could be 45° or anything else. But .5 is an easy multiplier.
There are other factors to consider as well. Time, how long does it really take to achieve one foot of depth? Once depth has been achieved & the fly comes under tension, which sink tip design will better maintain that depth throughout the swing? Or perhaps it is better that the fly rise up in the water column as it approaches the near bank.
The line having the fine taper design is limited to the use of the Versi Leader & therefore restricted to the use of smaller flies. The Versi Tip line, on the other hand, has no such restrictions.
Ask & you will hear pro's & con's on everything. The only way to know for sure is to try it for yourself.