Would you notice if 2 P225 65R17 and 2 P225 60R17 were mounted on a vehicle?

You would for sure notice if two tires of different sizes were mounted on the same axle. That for sure is a no, no. But I assume you know this are asking about mounting one size on the front and another size on the rear. Know that there is quite a difference in these 2 sizes. There is 3.13% difference in overall diameter. The 65 series tire in almost 1" larger in overall diameter. I personally would advise against this but if you must then mount the OEM size on the rear to keep your speedometer accurate.