Which type of cache is appropriate to your particular case depends on a
variety of factors including the hotness and other access
characteristics of your data set, the relationship of data set size to
the heap size, row size to key size, and so forth.

A little of topic, but I remember reading once from facebook that when a web user give focus to the inbox search box they sent a message back to warm the appropriate caches. I think it may have been in the original paper.

Out of interest is there a way to warm the key cache, other than say sending a get_range_slices command that asks for 0 columns?

I don't have a particular need to do this, just wondering.