I have a soft spot for the .444, but it seems to be slowly fading again. The .45-70 is probably the most versatile, with factory loads from pipsqueak to cape buffalo stompers available - of course if you handload the range is even wider. The .44 would make a nice companion to the pistol, but in my opinion doesn't offer enough of velocity increase in the rifle, especially if your intent is to shoot the same loads in both.
