IMO,the .405 is worth looking at.Factory 300 gr loads about 2400 fps.Woodleigh makes some bullets for the .450-400 of appropriatre dia ,designed for about the right velocity,at 400 gr.At proper .405 pressures it will go 1900 fps.Benchmark works in the .405
A whole host of cast bullets are available,and cast 400 or so gr bullets are a good match to the 1900 fps potential.
Another thing,the 405 is loaded IIRC,in the vicinity of 40,000 psi.The siamese is strong enough to step it up a bit
Playing with making cases for a 40-70 sharps straight,refering to the SPG lube booklet,I used to blow out 30-40 brass straight to make near 40-70 Sharps brass.Then we got blessed with Hornady .405 brass.It became silly to mess with 30-40.Consider 405 to be a lot like .303 and 30-40 basic brass.
I suppose you could neck it down;375,9.3,358,338,etc.Myself,I'd try to line up a bullet designed for a similar velocity so it will perform.
I'd go .405,standard dies,reamer,Hornady brass,300 and 400 gr factory bullets,cast bullet versatility.
And iron sights.Rainy day rifle.