Your results might have been different with H4895- which seems to handle pressures under it's prime area better than the other mediums, even IMR3031.

I have had good results with loads in the 60% range, using H4895, but that was in large case .45 cal. rifles, not small bores.

I find Trail Boss works a treat, but that 5744 might be as good or better and it is certainly capable of higher ballistics than Trail Boss.

That said, my .375'06IMp shoots amazingly well with 310gr. Case flat base bullets with Rooster Red lube and 18.0gr. TB - 1,380fps - about 200fps better than a .38/55.