No offense here. But wouldn't you find it 'boring' to use the same 300 grain bullet in your 54?
For instance:
I have two 1:28 MLs in 50-cal. Been thinking I want to shoot monster 460 grain conicals in my Knight and lightweight 200 grain sabot/bullet in my Omega. I also have a longrifle Shenandoah that covers my slow twist, roundball/patch fetish I get.
Why not conicals or a roundball in that 54? That's the Uno Numero #1 caliber for roundballs (my opinion). Why buy 54 cal plastic sabots to shoot XTPs 54/45 in a third ML?
Personally I would turn that 54 into a full-bore, all-lead / no sabot ML.