Spec:

E6900 4MB 3.20GHz 1066MHz FSB Q4 $969. us
E8000 4MB 3.33GHz 1333MHz FSB Q4 $1199. us (95 Watts)

As we see E6900 has 12x multi and E8000 has just 10x.
E6XXX serie can reach ~400FSB so its 400x12 = 4800MHz and hopefully new mobos with changeable voltage arive soon.

So is it worth to pay 230$ more for E8000 as we get lower clock?