Max Speed Vs. Wheel Size

This summer I had the opportunity to test my car - 1,000 break-in miles off a full mechanical restoration - flat out and see where its top speed came in. The one variable was that it was a particularly windy day and we had a headwind, but she maxed out below the stated top speed from the manual. I mentioned this to a tech at my mechanic's shop, and he responded, "It's because you put on 16" wheels with lower-profile tires than stock."

I understand the physics of how - all else being equal - smaller diameter tires will affect the top speed achievable, but here's what I don't understand from the online calculator tools (where you can only plug in speed, final drive ratio, rpm, and tire diameter): How do weight and horsepower figure into the equation? If I read this right, then a car traveling at 7,500 revs with a final drive ratio of 3.71 on wheels with an uncompressed profile of 24.5" will max out at 148 miles per hour, regardless of horsepower or weight. What if the engine put out 100 extra horsepower, or one removed 200lbs of weight? What am I missing?

 

That makes sense. Thanks.