Vref Ice is effectively Vref + 10 knots. To this approach speed should be added a minimum of 5 knots.
The latest revision to the B737 QRH (dated September 30th, 2002) states that "when Vref Ice is required, the wind additive should not exceed 10 knots".
This means that when using Vref Ice the approach speeds will effectively be normal Vref + 15 (minimum) up to Vref + 20 (maximum).