Top-end power... Wow! Where to start. I guess with how deep your pockets are?
A Rad Valve (Boyesen) is a great start to help curve the powerband into the top-end range. Also, FMF's Desert Pipe helped alot. Slightly retarding the ignition also helps, but be VERY careful in that regard as you can seriously hurt the engine. Those are in the $100-$200 range.
Also, again, your jetting is the cheapest way. I was also at a 168+ jet. But, if your pilot jet (low throttle range) is rich and your needle is rich, your top-end is going to be seriously weak. Start from the pilot (No throttle-1/4th throttle range) and find an idle and move up the jetting chain. Three MAIN parts of the carb in jetting is the pilot/needle (& clip)/main jet. Check out the jetting thread. It's long, but will go in depth on jetting.. Maybe skip to the end and read backwards, because the beginning is just us trying to figure out the issue I was having a few years ago.
OK, on to the real top-end stuff:
Bigbore - Make sure you port for top-end, or else the more displacement the more low-end you usally achive.
Porting - Usally comes with a bigbore. Make sure you want mid-top range.
Headwork - Cut for lower compression to give more topend range.
Crankwork for high RPMS (balance the crank so it doesn't fall apart).
PVL Ignition system.. Expensive but you will NEVER go back, it is crazy top-end power.
If you are serious about engine work, check out Ericgorr.com he $500 and you can get a 520kit, any port you desire, that includes plating, your choice of headwork, and a piston kit. Then it is like $150 for a hot-rod kit including your crank balancing.
Gearing: you will be fine stock. I'm 14/46 and happy with a 19in. tire right now.
