Did a spot of Googling for "LGB rack locomotive gradient" and came up with this: LGB rack locomotives can reliably climb steep gradients, often recommended up to 15% (1 in 6.6) on straight track when using dedicated LGB cogwheel track. While standard adhesion (non-rack) models struggle above 4-5%, rack systems allow for much steeper operation, with some setups working at 12% grades.
I have no personal experience.