Which is the best Hz when view 24p on Blu-ray?

[luscious]

The rest of the time the set refreshes at 60Hz.

Assuming the video is actually processed by the plasma at 60hz, that still would make for a discernible difference when playing PAL when compared to a true 240Hz LCD. And for gaming 240Hz is the way to go since frame rate for games is variable. Vertical syncing can alleviate judder for games but you pay a cost of a lower frame rate -- but that cost is reduced dramatically when you have a higher refresh rate.