8500 might refer to rpm's while in the cut. 10,000- 10,500 is usually what a 3400 will max out at. However the best way is to turn Hi needle so it 4strokes( sounds rich) out of the cut but cleans up while cutting.
Yep! I forgot to say, throw the tach away and forget about it. Tune it in the wood.
Tach's are mostly just for rev limited saws.