64bit mode is for supporting more then 16TB per Logical Volume (only for DSS), not for speed. With 32bit mode you can have multiple 16TB Logical Volumes with added Storage License Keys - (4, 8, 16, 32 and 64TB).

Single - 1 CPU

Multi processor - 2 or more (Dual and Quad cores)

TESTING mode runs 2.6.20 kernel version