How deep down the rabbit hole are you willing to go.
I reload 45-70 in BP loads, and via making my own BP, and getting lead free to cast, keeps the price way, way down to under a dime a shot.
Hence in BP loads, your around 1240fps with a 70 grs of F BP behind a 400gr bullet (where 45-70 got is name from, hence 45 caliber with 70gr of black powder). The only downfall, your are shooting BP loads, to be the end off the day, the gun needs to be fully stripped down to neutralize the salts so the gun does not rust out from the inside out.

As for PC coating, will solve the problem of 2Kfps loads that will not lead the barrel/will not need a gas check, so your looking for a bullet mold that dies not use a Gas check to start with.  In lee, the 340, 405, and 450 F molds would be a good choice, since they are gas check-less bullets, and do have a Flat point so your not jumping a country mile to leade with a load COAL that will cycle through the action.

Hell, I PC coat even my BP bullets just because, but still lube the piss out of the grease grooves with Bore butter, as well as run a soaked fiber patch in Bore butter over a nitro wad under the bullet (to keep the BP packed tight) for the same reason.  Hence bore butter keeps the BP fouling soft, so your not having to scrub as much between shots to get the hard caked fouling out of the barrel so the rifle will shoot tight again. Plus with the fiber wad and nitro was under the bullet, helps to reduce the amount of powder under the bullet to tune the load in for the gun.

As for smokeless powder loads, keep the load max pressures to that for lever action rifles (28K cups max), and make sure that the data you are looking at, is for a lead bullet (not a jacketed one).   Hence Lyman cast hand book 4th edition would be a good book to buy, and will find your best loads with 3031 (420gr at 1684fps), and only gain a few hundred feet per second over that of BP loads.   Looking at the 3rd edition since I have that in PDF, You can gain some speed with 4198, but had to use filler with this powder isntead. RL-7 is also a good powder if your looking for a touch more speed, but requires a filler wad as well.

As for BP loads, since you are working with available case volume, and the BP has to be in a compact state. pretty much straight forward.
https://goexpowder.com/wp-content/uploads/2018/06/cartridge-rifle.pdf

Don't shim, but instead polish out the mold if you need it to drop a larger OD bullet.
And as noted, PC coating will build up the bullet, so slug the bore to begin with, and then you only need to end up with the bullet OD sized .001" larger than bore in the end.

On the lee sizer's, I like to start with one that will size about .001" smaller than needed, then polish out the sizer ID to gleam it's sizing surfaces (will increase the ID about .001'), and still be able to polish out more of the ID if the bullet OD needs to be sized larger still.

Yes on PC coating, since it solves the leading problems without gas checks, since you can push the hard cast bullet PC coated over 2Kfps through a rifle barrel without leading problems.  With cast bullet, you need to be .001" over the size of the bore so the rifling get a good grip on the bore, and seals off to the bore as well.

Hell no on bore butter with smokeless powder loads, since it's only purpose to to keep the BP fouling soft.  It helps with non PC bullets to cut down on some leading problems with BP loads, but if you push a leaded bullet without gas check over 1300'ish FPS in a rifle lenght barrel, your going to get leading no matter what bullet lube you are using to start with.  
Bottom line here, bore butter in the quantities used for BP loads, causes a lot of smoke to begin with.  But them again, the BP causes a lot of smoke too, so a little extra smoke is not the end of the world. In a smokeless powder load, way better lubes even if your going to use wax for lube to help prevent bullet leading (again, no bullet wax needed with PC bullets, since the PC coating is preventing the leading problems instead, and your gaining some speed from the PC coating over a wax coating as well).

So PC solves the leading problem, so you don't need gas checks to begin with, nor do you need to wax the bullets.  
The downfall is really the casting molds, since if you cast a  gas check type bullet, then really need to use a gas check on the bullet to get the bottom sealing band, to get it to print well.  Without the gas check on a gas check design bullet, the back/bottom of the bullet has too much of a taper, and the gas behind the bullet as it's leaving the barrel without the GC sealing band caused all kind of problems.

So to sum it up, PC coating for the most part, is way better than wax coating bullet and/or using Gas checks.  The glitch, few bullet mold manufacturers have caught up with PC coating yet, so still pushing a lot of bullet designs that use gas checks isntead.

And the reason that I bring up for the most part, swaged bullets for target shooting, should not be PC coated.  The reason behind this, is the thickness/not uniformity of PC coating, and you don't want to add weight to the ID of the bottom of bullet as well.  So for swagged target bullets with knurled surfaces to retain the wax coating, leave them as is with the light wax coating.