Hi, from what i have heard, for general all mountain skiing you want the ski to be about up to your nose, and that is about 160 for me, so is a 168 all mountain ski too big?
Just tilt your head up. You'll be fine
There are more things to consider than height (weight, ability, style, type of ski etc) but as a rule of thumb, you're in the ball park. The other thing to realize is the 8 cm on an all mountain ski (depending on the make and model) can have less than 8 cm of running surface (ski snow contact) and 8 cm is just over 3 inches.