The sv_ladder_scale_speed value (default 0.78) in CS2 is indeed a multiplier of the player's base movement speed. The standard max running speed is 250 units/sec, so 0.78 × 250 = 195 units/sec is your effective speed on ladders. This applies to vertical movement; combining it with W+D likely increases the horizontal component, but 195 u/s is the base for calculations.
You can test exact behavior with a custom workshop map and a timer script to fine-tune it.
Doodle Baseball