Sorry, just read the caption of the thread. For a light Steel Challenge load with light bullets a faster powder would be better. I'm using N310 with all of my loads using bullets around 100 gr +-. The problem with light loads using slow powders is that they don't burn completely which leads to high velocity variations and causes them to be very dirty. Sometimes, grains of unburned powder interfere with the operation of the gun.
To give you an idea of what you might try, I have a SC load for my open gun using 115gr bullets and 3.8 gr of N320. To get an equivalent power factor with 3N37, which has a burn rate close to what you listed, I had to bump the load up to 5.5 gr. Both were 109 PF. In this particular case the combination worked pretty well but I wouldn't expect the same results with 100 gr bullet.