You will get closer extrapolating downward from Hodgdon's published data points.
Not just because they are published, but because the pressure will be more in the operating range you need. Nearer to the top a few grains will often make a big difference in pressure. 60% is way down the scale.
4895 is predictably linear within reason. You can use graph paper and draw the trend lines for velocity and pressure.
I keep my min loads around 40k psi. 4895 burns well in that range, and you need enough powder in the case to ignite consistently.
