Do you have a manual that lists the speer 170 JHC? I would take the data for that slug, back it down about 5% and start from there.
Data for the 170 grain stuff should be just fine, as long as you don't go right to the top of the charts.
You do have a chrono, right?
What gun are you using? Smith 57, 58, ruger, dan wesson, rifle?