There are a few factors affecting top speed.
- The factory 300 KPH (186 mph) limiter
- Aerodynamic drag of the bike and rider combo
- Weight of bike and rider and gear (only due to slower acceleration, which doesn't matter if you have limitless area to accelerate (Bonneville)
- Horsepower of engine
- Frictional losses of the drive train (chain, sprockets, shaft?)
- Surface the speed attempt was made on (pavement, salt, dry lake,?)
This is not an all inclusive list, but is the major ones. Tires can effect the speed as well. Even the unsprung weight of the wheels can have an effect on accleration, but not top speed. One thing I can say positively is that my 06 GSXR1000 will not go faster than 186 mph stock. Also, changing the gearing to a taller set up would do absolutely nothing(except slow it down), as it is geared for over 200 mph stock. That is pretty easy to figure. In my case at 70 mph indicated, my engine is turning close to 4500 rpm. Triple the rpm would put the engine at redline(13,500), so triple the speed is about 210. Some magazines check the speed at 1000 rpm in top gear and multiply it by the redline (I.E. 10 mph in 6th with a 13,500 redline would be 135 hypothetical top speed). Actual top speed varies hugely from hypothetical top speed. And you also have to remember that for whatever reason our speedos are way off on the optimistic side. My experience has been they are more than 10% off. Sometimes much more than 10%.
Sometimes gearing down rather than up will bring a higher top speed. The reason is most stock bikes will not pull top gear to redline. The aerodynamic drag on a motorcycle increases with the square of the airspeed. So it takes a hell of a lot more power to go just a few mph faster. If you can gear the bike down to get the rpm up higher into the peak power band of your engine, your top speed could conceivably increase. In my race bike's case, gearing down substantially did not affect my top speed at all. It stayed the same, but it gets there a lot quicker, and the engine is revving a lot higher.
I guess the moral to the story is the major influence, by far, is the drag on the motorcycle. If you can clean up the aerodynamics of the bike or tuck in tighter, you can have a lot bigger influence on top speed than adding horsepower. Unless you add a LOT of horsepower, like nitrous, supercharging, turbocharging, etc. Ideally you would have the most slippery motorcycle in the world, and have about 500 horsepower. Then you would be having some fun.