I think that FTX bullet likes a little more velocity than what I usually shoot from my guide gun or 458 socom. They shoot very well, but at lower velocity starting off, plus an even lower impact velocity, I just dont see them doing GREAT ever. They do okay, but not great.
Now if you push them faster and/or keep your shots closer before the speed gets lower then you might be happy.
Beartooth bullets makes some nice stuff if you do not cast your own and want to try plain ole lead.
I prefer a big wide flat nose cast bullet in the 45 70. Not going to get expansion with mine, but it does seem to work well, at least a handful of deer at about 60 yards think so. I have been playing with annealing the nose of the WFN cast bullet; no hunting experience with it yet, but it might offer a bit better terminal performance.
Barnes makes a jacketed bullet for the 458 socom, designed to work at low velocity. I believe it is an all copper "petal cutter" style bullet. I think it might be worth a look for you. 300g ttsx it is called. Have not taken deer with them, but they are supposed to offer expansion at low velocity. Currently messing with them in the SOCOM. I would happily try them at 1600 or 1800 FPS on deer. They are not cheap, but then again I doubt you would need to shoot too many as hunting loads. I just may have to load a few up for the guide gun this fall now lol.
As far as powder, h4198 does very well in my Guide Gun. RL 7 does the trick too. I load the cast bullets to about 1500 FPS and the lighter jacketed bullets to 1750ish. There is plenty more gas in the tank, but I dont like the recoil and the deer here just dont need anymore lol.