first think what u require ur PC for...r u gamer?? a graphics designer??
or just daily use??
then u can decide abt requiremnt of sli...
SLI means having two identical graphics card interconnected..so that u get double speed.
DEF=>Scalable Link Interface (SLI) is a method developed by NVIDIA for linking two (or more) video cards together to produce a single output. SLI is an application of parallel processing for computer graphics, meant to increase the processing power available for graphics. With SLI, it is possible to roughly double the amount of graphic complexity that can be handled by a computer just by adding a second identical video card
now u want best mobo for E6600 it would be
INTEL D975XBX2
ASUS P5WDH DLX
MSI D975X PLATINUM V.2...