The biggest recommendation that I have (pretty much the only one since I haven’t worked with a 3PAR in a while) is to ensure that your LUNs are sized correctly so that they are evenly spread out across all the disks in the disk set that you are using.
For example, if you have 100 disks in the disk set (I don’t remember the 3PAR term here), then you have 50 disks available (as the other 50 are the mirror). If you have a 1 Gig chunk size you want to ensure that all your LUNs are divisible by 50 Gigs. The basic math is ChunkSize*ActiveDisks then multiple the number you get until you get to the first size larger than the size that you need. You will end up wasting a little bit of space, but you will have a faster array.