Cyclone III – VCCIO of unused banks

You can of course file a support request to Altera and ask the question explicitely. The problem is however, that the support guys also have to rely on the device manuals and won't contact the developer staff as long as the manuals don't turn out obviously insufficient.

Or do a test on your own, carefully monitoring total device power consumption. If power down of selected banks works, I won't expect large power savings anyway. But I didn't need low power features in a Cyclone project yet.

It's interesting, that Stratix IV apparently allows bankwise power down. Thanks for pointing to this information.

Regards, Frank