When I did the Vetter Rally in 1984, I went to an industrial supply and got the largest front and smallest rear I could fix on my bike. I would not recommend this for the long term because those industrial sprockets are not as long lasting, but it worked for a single event.
If your bike is still pretty close to stock, you can go down several teeth on the rear or up one on the front and you will notice a difference. If you gear up too much, the bike will be harder to ride.
Back when I was racing motocross, I had a 2-stroke YZ400 with good midrange torque. I hopped up the engine and added one tooth to the front, and it was killer. I didn't save much gas, but it got big holeshots.
