Need to choose ASM performance for production database
ASM is not magic.

Each disk has a maximum number of IOPS it can support.  Each disk has a maximum throughput.  The more spindles (HDDs) you have, the more I/O you can get.  If one disk decides to take a permanent vacation and you don't have data on another disk.... I really hope you have viable tested backups.

From my tests, partitioning a single HDD into multiple LUNs and then using those LUNs for ASM will have a negative effect (albeit, ~-1%).

If you want performance, you will buy 6+ 500GB HDD (or SSD).  Each disk will have 1 LUN - the whole thing.  ASM will take care of the stripe and mirror.