I have driven 123 cars about 700,000 miles total, plus my wife probably went another 200,000 or so in them. So, I've been through MANY tires on them.

The difference in the 195/70 and 195/75 is about 3% in diameter, meaning only a 3% speedometer error, which means when your speedometer says 60, you'll really be doing about 61.8, not a big deal. To calculate diameter:

first number/25.4 x aspect ratio x 2 + wheel diameter

example 195/25.4 x .75 x 2 + 14 = 25.515
195/25.4 x .70 x 2 + 14 = 24.748

24.748 / 25.515 = .9699 or 3% difference

My best tire for these cars is a 195/75 Michelin XH. The 75 series tires are considered "passenger car" tires and are a harder compound. This means they last longer. Michelin tires are ROUND, not square like many other tires. If these cars were stiff suspended sports cars, a 75 series would probably not be what you want, but they are not. They are reasonably well handling sedans, and the 75 works great.

If you want a hair better handling and are willing to see many less miles out of your tires, then the 70, or even a 205/60(which I have run before) is what you want. If you want reliable, smooth running, long lasting tires, put on 75 series tires.

My $0.02,