"I'm designing for smaller spaces and wanted to see just how tight I can push the envelope while maintaining realism"
You can go pretty sharp on the curves with a 44 tonner. The Harlem Transfer in the Bronx New York( check out http://members.trainweb.com/bedt/indloco/ht.html) ran them around 90 foot radius which would be 22.5 inches in O scale. I've test run HO 44 tonners on 90 foot radius and they run fine. I've also tried S scale SW8 EMD with no problems. Here's HO and S 90 foot curves.....DaveB