Forum Moderators: open
As often: it depends.
Generally I would go for average 5-8 %.
I would mostly prefer to present content w/ KWs in a 'natural', readable form (as far as we talk on the white side). And mix in KW's in different phrases.
KW density alone is just one factor out of many, as you surely know.
My 2c.
Perhaps you already know, but there are many such discussions which you can find from [searchengineworld.com...] using the keywords "keyword density" :)
Admittedly, it's got a few good incoming links with the target keyword in anchor text, but still... :)
Cy