I think the 45 LRB is very capable in terms of accuracy and energy out to 100 yards for steel targets. While it can work out to 200 yards, performance falls off beyond 100 yards, largely due to the much lower ballistic coefficient of the smaller/lighter 45cal ball. Looking at my 58 cal(279gr) load at 1400FPS compared to my 45cal(133gr) load at 1700FPS you can see the effects of the 40% higher ballistic coefficient of the 58ca(.09BC) to the 45cal(.06BC). Both rifles will produce comparable accuracy/precision. Using a 50 yard zero, the difference in drop between the two at this range is less then an inch, 45cal(4.9”), 58cal(5.7”), The initial gap in velocity evens up at 100 yards with the 45cal at 997FPS compared to the 58cal at 992FPS, even with the 300FPS difference at the muzzle. Additionally, with a 10mph crosswind, the 58cal drifts 8.5”, compared to to the 45cal at 12”. The energy difference at 100 yards is 45cal(280FPE) about half of the 58 cal(610FPE).
At 200 yards the drop between the 45cal and 58cal is the same(45”) with the velocity of the 58cal(830FPS) passing the 45Cal(760FPS). The heavier 58cal has almost 3X more energy(425FPE vs 170FPE) at this distance. The wind drift performance of the 58cal widens further with the 58cal at 30” compared to the 45cal at 43” in a 10MPH crosswind. While the OP is comparing a 54cal, its values are roughly within 10%(less) of those shown for the 58cal.
Apologies for all the ballistic mumbo-jumbo. Given all this, I have a great deal of success and fun shooting steel/targets both my 45 and 58 cal rifles at the longer ranges. Regardless of which is used, IMO, far more influential in hitting at the longer ranges is distance judgement, hold-over skills, and the ability to read and hold for wind correction. I would have to say that, all things being equal, my on target hits and knock downs on steel at long range are notably more frequent when I use the larger caliber LRB/rifles due to the ballistic advantages. The disadvantage is greater recoil....a consideration with some shooters.