fuel additives

[Festively Jolly]

hey guys. i was wondering if any of these work.  whether for injector
cleaning, gas saving treatment, octane, etc...

what is the point of putting in an additive that boosts your gas 17
points?  i think engine on the 88 Audi 90 is 92 or 94.  i can only find
91 ron around here.  so is 108 octane better for the engine or make it
run better?  

i put in this STP injector/piston top cleaning/octane all-in-one booster
and it seemed to burn the gas rather quickly and it acquired this new
loud "tick" noise that gets faster as the engine revs.  makes it sound
pretty crappy.  is it my lifters or something?  what can i do to get rid
of this noise?
well thanks group.