Isn’t slew rate a function of the amplifier? Not the conductor. The advantage of silver is that the resistance is lower. Maybe someone should come up with copper-plated silver wire.
Yes, but the conductor does play a role. All cables act like some sort of low pass filter. If you model out a simple resister and a cap as a low pass filter, the higher the resistance will result in more low pass filtering. As you said silver does have lower resistance so the rise time won't be degraded as much as copper. In some cases having a higher rise time improves jitter but high rise time will also result in higher EMI. That's why most high speed data rate will have only enough rise time to get away with. It's a balanced act so it depends what you want to achieve,
Also as I mentioned, there is no one single factor. It depends on the situation.