I've never found drifting/sliding to be faster in LFS, and it shouldn't be in real life. The tires provide maximum grip with a certain amount of slippage of the contact patch, and when you go past this grip declines making cornering speeds slower. You may have an understeery setup that needs the slide to get pointed correctly and are gaining time there.
You can test this on a skidpad or AutoX course. Tweak a setup until it is neutral then accelerate while turning. Then hit F9 and watch the lateral G display at the bottom. It will rise until you break loose. You'll be surprised how much grip you can actually get without breaking loose. I always watch the F9 G display when learning a new track. I know the capability of the cars, and that helps me maximize my driving without the seat-of-the-pants feel.