i will never understand the obsession with big locomotives. a Std Gauge GG1?... at 1:26.6 you're looking at a locomotive 36" long. about the only Christmas tree that would look good running around would be in Rockefeller Center. looking at steam, i'd like to see a ten wheeler... a 4-6-0. it would be the least expensive way to get to a 6-wheel drive configuration while likely being smaller than a 400e. ten wheelers were also for the most part dual purpose locomotive which would look equally good pulling a short freight, a passenger train or a mixed consist.
a good next step would be to take the same boiler and design an 8-wheel (w/ smaller wheels for freight) drive creating a 2-8-0 Consolidation or a 2-8-2 Mikado type. blinding the center drive wheels on both the 6 or 8-wh drives would still allow for tight radii, but would also look good on newer 72" diameter standard gauge curves.
women have had the right idea for years ... good things come in small packages.
cheers...gary