Both casinos are good Buddy, fortunejack is a reputable casino well known on this forum, I personally have never played with such amount of money as you mentioned, but there are many withdrawals from that casino worth up to hundreds of thousands of dollars (if not more) without issues, so trust that, this is one of those casinos you can really trust.

And for Rollbit, it's also a trusted casino, though there have been some complaints from customers about this casino here and there, but I believe they are still good, and you can safely withdraw a really huge amount of money from this casino without issues, and even if issues rise up, trust that it will be resolved amicably as long as you post about it on this forum.