The peak current in the diode is what was flowing in the inductor just prior to the switch opening (250mA) . The peak inverse voltage applied to the diode is the power supply voltage. To be most effective in preventing EMI to other circuits, each solenoid should have its own diode, and the leads between the coil and it should be as short as possible.
With a snubber diode across it, I worry a bit about how long the solenoid will take to release. Try it and see if the diode causes the solenoid to hang in too long. If so, there is another way of suppressing it which will release faster.