We used to only put N45 strength magnets in sliders - it was a nice, balanced middle-ground.
But here's the cold, hard truth...
We would get emails saying they were too strong ...AND ...we would get emails saying they were too weak.
After many years I got to understand that sliders are VERY personal. The style, shape, size, weight, plates, material, magnet strength ...and so on.
The best solution is to put the magnets in that feel the most optimal for that slider ...and, if it doesn't feel quite right for the customer, they can switch out the magnets themselves.
We typically use N42 and N52 (but also N45 and N48 sometimes).
Here's our "ugly but practical" magnet store and dispense station. We designed and 3D printed them in-house. It's a simple solution - but the life-improvement feeling is a solid 10 out of 10! :-D