Hi William welcome to the YOC. As you have already figured out changing the gearing on your bike will give you a top end boost but not a lot, the real problem is that your bike was designed to go at a certain speed and your going to find that getting it to go much faster will get expensive very fast, exhausts and carb kits plus boring out the barrel will help but every time you increase the speed the reliability will go down till you reach the time when it detonates across the road and throws you into the nearest bush if your lucky. Your best bet, take your test and ride a bigger bike..! Sorry mate but there is no magic fix for your problem. Now your other problem with going through sand at speed, again you can't, it's the same as the bikes and cars that do the DAKA rally even they slow down for sand.