Charles exactly. you proved my point. 3600 rpm, regardless of the HP, is still 3600 rpm. you end up at the same top speed. it's just how fast you get there. your point is CHANGING THE GEARING. that wasn't the question here. that part of the equation was a fixed, as is the rpm. which means the top speed is the same. really the only variable is time to get to that speed.
You're still saying "how
fast you get there", which in incorrect, it should be quick/quickly. Fast relates to velocity/speed, not elapsed time/acceleration. Quick relates to elapsed time/acceleration. A vehicle can be quick but not fast; a vehicle can be fast but not quick; some are both quick and fast. Yes, I'm critiquing your terminology, which some would consider rude, but if you want to be clear and avoid confusion, you need to use correct words/terms. It's like people who call a high ratio a low ratio and vice versa, a common mistake, and it causes confusion. This is constructive criticism, not an insult, and I hope you are not offended by it.
No one said they had to run the same ratio, but if they did, as I said in my previous post, the 5 HP engine may be able to reach 3600 rpm while the 3 HP may not and thus not attain the same top speed; in that case, the 5 HP would be faster. Also, with the same ratio, the 5 HP, mainly due to more torque, would be quicker (reach a given speed in a lower elapsed time). Consider that many people change their final drive to a lower ratio, usually by installing a smaller rear sprocket, when they put a larger/more powerful engine on a minibike; it's quite common. Summary: More HP = faster minibike.