Ah, i remember back in the good old days, only people with actual knowledge would post. A thread would be over in about 12 posts because the topic question was clearly and concisely answered.
Basically, a 3K isn't necessairly faster than a 4K and vice versa.
I have a mate who has a 3K KE30 and it is pretty slow.
My old 4K was slow when i first got it. Remove spaghetti, replace air filter, replace spark plugs, points, condenser and give it a good old tune, and she flew quite nicely.
Some motors are just quicker than others. Mileage, age, care, servicing etc has a lot more to do with how well an engine goes than the statistics on paper.