I know the Big Boy (4-8-8-4) looks neat, but, as was stated by others, the question is what will your minimum radius curves be? I'm not so concerned with a locomotive "chasing its tail" around a small layout, but whether the loco will successfully negotiate its way around the curves and through #6 turnouts. A number of the larger HO scale model locos are listed for 22" radius minimum. If you must go tighter than that, but want an articulated locomotive (that is one with two sets of drivers under one boiler, you might want to look for a Mantua logging articulated, a 2-6-6-2. Mantua 4-6-2 Hudson, although recently discontinued, can still be found with DCC and sound installed for a reasonable price. If you want, and can find a 4-wheel trailing truck, you can easily convert one of these to a 4-6-4 Hudson type. These will reliably go around 18" radius curves, and possibly even 15". If you can build larger curves on your new layout, then you can go with larger engines. Best of luck!