Yes, combining members into a single pool can increase performance.  Especially if you use HIT/ME, HIT/LE or with proper ESX license,  MEM.   This optimizes MPIO especially for multi-member pools.  The data for each volume is striped across the available members.  This means more cache, CM resource and drives are working for all the volumes in that pool.   Also with current firmware if one member if busier than the other, the will swap out pages to bring the latency back into parity.   No, you can't use non Dell drives in a 6000/6100 series arrays.   If you have been using non-Dell drives with your 5000/5500 you are very lucky.   Especially with longevity, recent firmware from the drive vendors have addressed a number of issues with premature failure of drives.   The firmware update utility would not work on non-Dell drives.  Regards, 
I’ve had some 5000/5500 units in production for many years and have been quite happy with them. The one thing we never did was “stack” them into combined storage pools. I’m wondering if people have had experience with this and if there were significant performance gains   Related to the 6000/6100 series, I was hoping to get a definitive answer from someone here regarding the use of non-dell drives. I’ve had zero issues with my 5000/5500 units but there seems to be a great deal of conflicting info online regarding this.   thanks
Two questions about equallogic 5000/5500 and 6000/6100 series