Bill Blackwell
Leica M Shooter
The answer is in which camera you reach for first when you go out to shoot.I almost never take the MR4 meter off. Very accurate meter and very quick to use. ... I had an M6, bought new shortly after it was introduced. That's one camera I really didn't bond with. ...
It seems to me like you'd miss the M4 if you gave it up. Plus the M7 will fetch the most in the used market today. And based on what you'd likely get for it (pennies on the dollar compared to what it sold for new), I'd never let the M9 go. I'm assuming you got the sensor replaced?