You're going to be on the rev limiter a fair amount at that track. I would pay attention to your RPM on the second longest straight. You certainly don't want to be in the rev limiter on the 2nd longest straight, maybe shoot for 5800-5900 on that straight.
"Gear bound"?? I've been in karting for 50 years and don't know what that means.
Assuming this is the controlled LO206, there's an RPM limit. I would want to reach that limit that about 3/4 to 7/8 down the main straight. Gear accordingly.
Driver size; at this point in your driving career I don't think it makes a whole lot of difference. Just get the overall gear ratio right.
Make sure the clutch is holding the engine at peak torque coming out of the corners. Very important.
Find out what trail breaking is, avoided if possible.
Learn about air density versus jetting. Very important.
It's learning to drive is just as important as learning a set up. If you achieve proficiency in less than a year. It took me 3 years. I loved karting so much I stuck with it, eventually learning how to drive and how to tune.
Tuning; air density and jetting go hand-in-hand. I have this idea tuning is's severely limited as far as tuning with the L0206. Work with it.
Not all L0206 engines are created equal. There's good, there's bad and in between.
If a track requires say a 16/60 for Clone to turn 6800 rpm, and you show up with a 14/60 because it worked at the last track you ran, you would be gear bound as your trying to turn the motor 800 + rpm over it's target.
The position of the engine after moving it minimally to accommodate the smaller gear is NOT going to change your RR percentage very much if at all. I've made bigger changes and seen minimal change on the scales.
A kart set-up is usually a compromise between being fast on the straights or being fast in the back field. You have the right idea in changing gears, now check your lap times to see if there is a noticeable change. As you get more seat time, roll the corners faster and your racing line improves you may want to remove additional teeth from the rear sprocket. As always keep good notes and know that you will be forever adjusting your kart to changing track conditions and your driving style.
As far as which gear works best for your specific kart and level of experience you can go to a 206 kart race at that track and ask the fast guys what gear thy are using.
Off the cuff 19/66 is a decent place to start. You can consider the QPT engine mount from fastermotors.net to make rear gear changes much easier.