I totally agree with you about the sheer size of these things, after all, at one time I had five of them - just for fun. Just the one now, with Aristo's add-on sound system, controlled from a hand-held panel between tx-er and track. I still have four SD45s though - the two imaginary war-bonnets, a CPR golden beaver and a Shawmut Car Shops custom-paint NP.
The GP40 is a popular US loco here, as are the many colour schemes of the GP38 - a VERY fine loco - mine is in war-pumpkin scheme, my all-time favourite.
There are many layouts over here in lil'ol' England that can run a train of fifty or more cars - our own at our ride-on track is but one - the Cathedral Mountain track on these pages is another, and I can easily find another twenty without trying too hard. One railway I know of, but have never visited, has a track that takes seventeen minutes to go round, surely big enough for most folks... anywhere.