Awful performance. In specific: constant FPS drops which make the game a slide show. It's not a throttling, it's not a route specific. It lags even on empty tile which wasn't a case for build 5.5.
Moreover, that lost frames impact also scripts execution bringing delays to them.
The majority of Ukrainian community experience that, so they had to roll back to SP5 version to play instead of struggling.
And my system is powerful enough to run other modern simulators smoothly on high graphics settings. In the same time, Trainz keeps using 20-40% of its capacity lagging, freezing and annoying.