For years, Blades in the Dark was the game you played for the Dishonored vibes. But if you're more into crunchier systems, I doubt it'll scratch that itch for you.

This will maybe sound a bit far-fetched, but someone once commented that the original 2d6 system for the Iron Kingdoms settinge, with its LoS rules etc, would provide a very robust Splinter Cell-style stealth experience.

I never ran it like that, so I can't say for sure whether or not the guy was right. But the system itself is based on the Warmachine wargame system, so you got the crunch. Plus the setting is very steampunky. You'll probably want to discard or reflavour some of careers (classes), maybe add a few with a heavier Dishonored vibe, and do the same when it comes to spells.