my estimate is 35-40% (thus being the strongest factor already). what would you think? (feel free to post your percentages, i don't have too much SEO experience)
that's one possibility but my thoughts were even simpler: i simply differentiated between the number of search keywords. i think a single keyword doesn't provide any context (whereas two already give some) so it needs PR and off-page factors as a cruch. the more keywords somebody searches for the more one-page factors may be valued. i.e. if somebody searches for an entire 10-word-sentence a PR2 page having the sentence as title is probably more relevant than a PR8 page with the sentence somewhere in its body.