The effect of the groups at para position on SN2 reactivity
This is what I found from your reference to Clayden. You just had to read the next paragraph ( I have highlighted the point ). You can see that March and Clayden have agreed on the same point, that electron withdrawl from the phenyl/allyl group increases the effective conjugation in the transition state.
So I hope You can understand what will be the correct order and why.

P.S. I know this question is old, but it was unanswered, and someone may benefit from an answer.

Reference: Jonathan Clayden, Nick Greeves, S.Warren, P.Wothers -Organic Chemistry (2000) - Pg 422.