Superdome 2 expansion options

We currently have a Superdome 2 server with 3 i2 blades configured in 1 partition. We need more processor power, so we are wondering about our options. Can we still purchase i2 blades or only i4? Can an i4 blade be configured into the same partition as existing i2 blades? Can i2 blades by upgraded with the new i4 processors? Can i2 blades be traded-in for i4 blades?

Thanks,

Randolph Knippel