The DA trigger pull will vary from gun to gun, and could be altered by having a trigger job done. It would not be unusual for a trigger to weigh 12 lb in DA, but can be lowered to around 7 or 8 lbs. Don't go too low as reliability will be a problem. Most competition shooters use Federal Primers as they are the easiest to go off with the least hammer fall. The barrel length is a personal decision, and only you can make that determination. A 6' barrel gives you longer sighting radius and therefore improved accuracy, but you may find front end heavy. A 4" comes out of a holster faster, but has shorter sighting radius. If you are concerned about making power factor, the 6" barrel will give you more velocity from the same loads, which will result in a higher power factor. My personal preference would be the 5" barrel as the best compromise. For shooting steel, I assume you will be shooting 38 wad-cutters, which have a minimal power factor, but the best accuracy, be sure to thoroughly clean the chambers after shooting to keep the carbon ring build up out, or you will not be able to chamber the longer .357's when you want to. I have a 6" 686 (no dash) that I have had for over 25 years which measures a 9 lb DA trigger pull, and it is 100% reliable with any primer. 25 years of use have smoothed it considerably.