Don't get caught up too much in the R5 penalty. It certainly is a bigger hit than R1/R10, but I've run SQL Server databases for years on R5 and it has worked well.

The resiliency is a big deal. I've definitely had issues where we lost a drive and another one in a week. Not having a spare that rebuilds quickly is an issue. I'd honestly be more concerned about that than performance. If performance suffers, re-evaluate.

However, you need monitoring. You need to know the IOPS you get now, the latencies from the various files (from DMVs) and read/write levels. Once you have that, you can re-measure with a change and decide how things are performing.

I prefer R10 for everything, but R1 works well. We used to run SQLServerCentral with R1 for OS, R1 for data, R5 for logs/backups. 8 drives.