I just recently purchased the Niagara and can run it (carefully) on a layout that has a couple of turns that are less than 18" radius. Low speed around the curves is important (ha, try telling that to my grandson). My layout is very small (actually folds up into a basement wall, that's why I always drool over those enormous layouts in magazines. The tender is more of a problem than the engine (it's one of those centipede designs and doesn't do well around tight curves but from what you say it may be ok. I'm thinking of buying a different tender to ease this problem.
Paul
Paul