Sizing the ODA

HI Gurus,

My question is more of presales , how do we size the ODA  ? 

From an  AWR perspective we can understand reads and write ratio. But for example  if certain database environment on Intel had 8 cores and if the customer would move to ODA can we half the  core requirement since the writes happens to SSD and reads happen from SSD.

I appreciate the guidance on the matter

regards

Moncy