Question on Exadata X8 - IO

We are currently having HIGH redundancy(triple mirroring) for our existing X5 machines for DATA and RECO disk group and DBFS is kept as NORMAL redundancy(double mirroring). Now few folks raised questions on the impact on IOPS and storage space consumption, if we use double mirroring(NORMAl redundancy) vs triple mirroring(High redundancy) in the new X8 machine. I can see the benefit of double mirroring(Normal redundancy) being saved in storage space(around 1/3rd in terms of DATA and REDO copies), but then what is the risk wrt data loss, is it okay in a production system? (Note- We do use ZDLRA backup for taking the DB backup. And for disaster recovery we have active data guard physical standby in place which runs in read only mode).

With regards to IOPS, we are going with default write back flash cache enabled here. Is it correct that with double mirroring we have to write/read into two places VS in triple mirroring we have to do that in three places , so there will also be degradation in IOPS with triple mirroring/High redundancy as compared to double mirroring? if it's true then by what percentage the IOPS degradation will be there? And then if it's okay if we go for double mirroring as that will benefit us wrt IOPS and also saves a good amount of storage space?

Regards