It is hard to say and best to check for other threads on BRM and how to apply it well. always try to think it out and use common sense.
Your 30% roi is great but a small sample but you will have built up a decent roll if you haven't extracted much or blew it on cash PLO or something
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You can lever your bankroll more if you are willing to easily jump down if things go wrong.
The best strategy is different for different players, some are ok just mixing games others get overly anxious about the high value ones and don't play their best.
180's do need a large BR and lets say your real roi at the $2.50 ones was really only 20% and perhaps at the next level $8 you could reasonably expect 10% I would jump up to all $8's at perhaps at $1400 and then fall back down to the $2.50 at about $1000. This allows for about a 50BI loss or cushion at this $8 level, usually you should cash in some so it's never as bad as just 50 games and should be enough to try to get your $8 eye in. In fact you should win at 10% but things very often don't go to plan
This may seem like a large BR to keep at the $2.50 but things can easily go wrong and jumping to a new level ~3x the cost can be hard.
If you are happy mixing levels it is easy to keep throwing in a few games and hopefully eventually scoring enough to play all $8's.
Think it all through and find an approach that works for you.