Should I leave?

Hi guys,

Long-term lurker seeking some advice, thank you for the wisdom in advance.

I'm currently an investment professional at a T2 investment firm (think solid, but not stellar). The team is relatively secure, I'm a decently good culture fit.  I'm with a manager whom is currently okay with me, but has historically been quite merciless in firing people he doesn't like. Some of them are actually pretty good performers but he got rid of them too. 

I got an offer to join a Tier1 firm (better investment record and quality) - culture expected to be a lot worse / intense, and skill-level would be a step up from where I am now, so I would be taking a career risk. That being said, my current firm is a bit staic and the manager I'm working with seem ruthless when he doesn't like you, so I'm not sure if that's as stable as it looks in the long-term too.

Old job = secure currently, with a manager who has been ruthless to others before me (I suspect it will recurr). Historically when someone on his team tried to move to a different team internally, it ended poorly for the person.

New job = more intense / demanding and thus less job security, unclear on culture fit (haven't worked there so hard to say. Ref check seems to indicate brainiac / hierarchical culture)

How would you decide?