This is the currently known new combat xp table:
https://runescape.wiki/w/2023_changes_to_combat_experience
However, Mod Sponge has already said they will continue to change some mobs post Necromancy Launch:
"That being said post-launch, I may look into adding XP mods to some monsters (things that come to mind are things like mammoths that force you into 1v1, or are slightly more awkward to AoE etc.) To make up for the changes (though, they weren't remotely competing with something like abyssal lords previously, they could be in a better spot.)"
https://www.reddit.com/r/runescape/comments/15b51x9/necromancy_insights_combat/jtsdsjd/?context=3
If you are eager just to train Slayer now, perhaps you can use the current combat xp table for guidance. However, I think it probably worths to hold onto your Slayer Wildcards for now, especially there are plenty of Necromancy content and likely new Necro mobs coming up with bigger xp and rewards.
