I pretty sure we all know that larger wheels change the speedo, at least if you do a search you will. Basically what your saying is that due to the larger wheels, your actual speed will differ from what is shown on the tach and speedo. I still don't see where gear ratio's are coming in, your just explaining the speedo concept again.

edit: Going from stock 15's to 17's with a 215/45 tires will yield a 1.7% change. At 60mph on the speedo, I'll be going 61. And as you go faster, the difference will increase.