Let's see if I can avoid talking us further into a hole . Do you take your example from the manual (e.g. rpm range for the engine between 2000-16000)? My understanding is that those #s represent the theoretical range the engine can run at without something bad happening (and yes the 2000rpm won't be at full throttle).

The actual rpms you will be able to achieve can be quite different as they depend highly on which prop you use, atmospheric circumstances etc. So using a tac to try to get your engine as close as possible to 16000 rpms and then leave it there is probably not a good idea.

Also I think tacs are more used to tune 4 strokes, they're almost mandatory for 4 strokes as right mixture setting is very important and running your 4 stroke too fast (too high rpm's) is surely going to break something and they are more difficult to tune just based on listening.

If the above didn't help surely folks more knowledgeable than myself can provide more detail.