I see serious problems with taking a RAID chart from IT guys and accepting it as being applicable in any way to SQL Server. SQL Server requires almost the exact opposite of what IT likes to implement for their file servers. The RAID chart says RAID 1 (mirror) is only "good" at both reading and writing when RAID 1 is the fastest for general SQL Server apps. What I've found is sql server needs a setup optimized for 8k random reads and writes and you can and should ignore virtually all other disk ratings. An SSD will perform between 10x and 100x better than mechanical disks. Hands down, RAID 1 will perform the best for SQL Server but most of my customers have chosen the worst setup of using RAID 5 and then blame me when their RAID is 4x slower than my laptop performance of no RAID.

Actually, having many RAID 1 arrays is the best solution. Having many separate I/O channels will dramatically speed up SQL Server.