ASSM and high volume concurrent inserts

A client is running an application that does high volume concurrent inserts (> 200million rows). Performance degrades with high buffer busy waits. The tablespace is ASSM managed, so we can't change the freelists to tune it. I want to try moving to a manually managed tablespace and tune the freelists. But not sure if the client will go for that change, given the effort and timelines. Has anyone come across performance issues with ASSM and high volume inserts? Anyway of tuning it with ASSM?

Thanks in advance,
Haroon

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